1. The consequences of Newt drifting with the Kaiju Hivemind
The subplot of Newt and Herman drifting with a Kaiju is the best kind've sequel tease, in that it serves an actual function in the plot and leaves no gaping loose ends, but still has enormous potential to be expanded upon. These are now two characters who have a unique connection to the Kaiju. Was Otachi really after Newt specifically, or was that just speculation on Hannibal's part? Do they want him dead, or do they want to take him alive, & if so for what purpose? Assuming the Kaiju Masters are still around, is Herman now also a target? How have they been changed either mentally or physically by the experience? I could imagine this leading Newt particularly down a rather dark path. Seeing as he already has a vaguely disturbing fanboy obsession with the Kaiju, having one inside his brain could seriously mess with his head. I'd wouldn't be surprised to see both Newt & Herman figure in more centrally to future sequels because of this.
2. The consequences of the Jaeger program going rogue
One minor quibble I did have with Pacific Rim upon repeated viewings was that the Jaeger program being decommissioned had little to no effect on the actual plot. We never get the feeling that they're running particularly low on resources, and apparently the world governments do not mind that they are acting without authorization, using equipment built with their money*. I'd like to see the fallout of the PPDC going rogue dealt with. Now that the Breach is sealed, will the Jaeger program still exist in any form? What about the failed Wall of Life? Surely people are still upset that their leaders were prepared to abandon them and leave them with an obviously useless defense. I'd like to see the early hints at social stratification given a little payoff. Are people still rioting? Are the rich and powerful still cowering in their safe zones? I was hoping to see an attacking Kaiju deliver a little poetic justice against those assholes, bypassing the pacific cities to go further inland and show them just how "safe" those safe zones are. After all, the Kaiju are taking orders from intelligent beings, it'd make sense for them to go straight for the leadership.
3. New Jaegers & Kaijus
Guillermo has already said that we'll see "Gypsy 2.0" which is fine. Gypsy Danger is more or less the face of this budding franchise, so it makes sense to bring her back for Raleigh & Mako to pilot. But I don't want to see rebuilding old Jaegers to become a trend. I don't want Crimson Typhoon 2.0, Cherno Alpha 2.0, or Striker Eureka 2.0. Especially in Cherno's case, since being so old and outdated was part of the charm of that particular Jaeger. Those were all awesome robots, but a sequel should give us new things, not recycle old ones. I want to see new Jaeger designs with personalities all there own. I want new and interesting characters to pilot them. I want to see other pacific countries get Jaegers of their own. Given who's directing, I'm surprised we didn't get a Mexican Jaeger or even a Peruvian Jaeger (I know I saw a representative from Peru among those chewing out Stacker). Central or South American representation was surprisingly lacking this first time around, considering they'd be on the front lines of an invasion from the pacific.
4. More variety in the characters
A small nitpick, since comparatively Pacific Rim had a much more diverse cast than an average American blockbuster, but it could be better. Mako Mori was a great and rather unconventional female character, but she was also the only female character (excluding Sasha Kaidonovsky, who I'd really have like to see more of). The prequel comic Tales from Year Zero had a few lady characters to offer that I could see showing up in future sequels, such as Caitlin Lightcap or Naomi Sokolov. And with the exception of the half-Peruvian Tendo Choi, there is (once again surprising given who's directing) a noticeable lack of Hispanic people among the mostly Asian and European cast of characters.
5. Mako getting a new hairdo
I'll allow you to look puzzled by that odd-sounding request before explaining.
Okay, now I'll explain. As you doubtless noticed, Mako has streaks of blue in her hair. The choice of blue is a rather interesting one for the costume department, and one I have a hard time believing wasn't intentional. Blue is by far the most significant color in Pacific Rim. Whenever it shows up, it typically means one thing: Kaijus. Their bodies glow with it, they bleed it, wherever they go, blue follows. But more than that, it means death and decay. It's the toxin they leave behind, the way they taint everything they touch. Even after the monster is gone, it leaves its venomous stench, corrupting and killing anything left behind. So I find it hard to believe the blue highlights in Mako's hair aren't representative of that. She survived her first encounter with a Kaiju, but it left her scared, tainted, poisoned if you will, by fear and hate. To see the highlights gone or replaced with a different color would be a great visual cue for her ongoing character development. And I do want it to go on. I want to see how Mako has grown since the ending of the first film, now that she's achieved her life's goal and no longer needs her mentor. I imagine she'll be far more confident and commanding, very much her father's daughter. I'd love to see her give a Stacker-esque speech at some point. I'm quite sure cancelling the apocalypse runs in the family.
6. "You can always find me in the Drift!"
Speaking of Stacker, you might remember those as his last words to Mako before he died. A heartbreaking goodbye to be sure, but I can't help but wonder how literally he meant that. Obviously I don't wanna see Stacker brought back from the dead, that would completely negate the ending of his story. Stacker Pentecost went out like a boss, and that's how it should be. But I feel a Pacific Rim completely devoid of the Pentecost brand of awesome would be poorer for it. I could easily see him returning Ben Kenobi's ghost style, appearing to Mako during a neural handshake to offer counsel at a moment of uncertainty. It wouldn't actually be him, of course, just Mako's memory of him, or her concept of what he might have said. But any excuse to get Idris Elba back in this mother for a scene or two, I say.
7. A good Kaiju
I admit it disappointed me a little that none of the Kaiju had quite as much character to them as the Jaegers this time around. Oh, they looked great, the designs were awesome, and the names they gave them certainly helped make them memorable. But none of them had much personality of their own, they were just mindless soldiers serving an unseen power. Maybe that's the problem, that they were under someone else's control as opposed to being agents of chaos and random destruction born from man's hubris like the classic Kaijus: Godzilla, Rodan, etc.
My point is that as cool as they were, I don't feel they'll have much longevity as individuals. I doubt anyone will be clamoring for the return of "Knifehead". A good way to make one of the Kaiju a memorable character? Introduce one as a good guy. The baby Kaiju raises interesting questions about what might've happened had it lived. Were they to capture a baby Kaiju alive, could they potentially raise & tame it, perhaps even train it to fight alongside the Jaegers? Imagine Gypsy playing fetch with a lovable Kaiju with the personality of a faithful dog. I know Newt would be all over that. At the very least the guy deserves a pet skin parasite or something.
8. More of the Kaiju culture
Pacific Rim did a great job with world-building, giving up tantalizing glimpses of details of this future world that could very easily be expanded upon. You could probably build an entire movie just around Hannibal Chau and the entire premise of a "Kaiku Black Market". It'd be like The Godfather, but with giant monsters. And it raises so many questions. Since they've figured out so many different ways to use the consumption of Kaiju body parts, they must've gone through a lot of experimentation to arrive at that point. So what kind've things resulted from that? Surely a lot of those experiments when wrong. Are there human/kaiju hybrids running around, the unfortunate result of Chau's experimentation? What about that cult of people who worship the Kaijus from inside that hollowed-out skeleton? Do you think they ever make human sacrifices to the Kaijus? I could imagine some monks sitting and praying directly in the path of a rampaging Kaiju.
9. More about the Kaiju masters
This one is pretty much a given if there is indeed a sequel, but it's worth mentioning. For there to be anymore to the story, the mysterious other-dimensional conquerors that created the Kaijus with almost certainly be back in some form, and it would be nice to learn a bit more about them. Will any of our main characters ever meet one face to face? Will they personally visit Earth at any point? How many other planets have they invaded, or even other dimensions? All they all evil, or are there good factions within the race that oppose their colonialist actions? Do any of their Kaiju creations ever rebel? Are they the only factions out there with giant monsters at their command?
10. A Power Rangers crossover
Hey, if Guillermo can talk about a Godzilla crossover that will never happen in a million years, I'm allowed a ridiculous fanboy request too. After all, the now-in-young-adulthood Power Ranger generation likely comprised most of Pacific Rim's American audience. So let's see the PPDC up against Rita Repulsa. Let's see Gypsy Danger and the Megazord cross swords before teaming up to punch some monsters. Who wouldn't want to see Staker Pentecost meet Zordon, or Kimberly Ann Hart (yes, I know her character's full name, what of it?) meet Mako Mori? You know that Alpha 5 interacting with with Newt and Herman would be a riot. Sure, the PPDC would be a little out of their league with the hand-to-hand stuff (though a sparing scene between Tommy & Raleigh would be a must). But seeing the Megazord brought to life by those glorious modern special effects would be worth the price of admission alone. Plus, it could make for a great setup for that Power Rangers movie Saban keeps saying they're gonna make.
*I did notice on the 3rd or 4th viewing that the UN council said they'd still be funding their operations for the next month before cutting them off, meaning Stacker hasn't gone rogue exactly. My point still stands, though.