Unabridged thoughts:
As an antagonist player, I'd like to see abilities restructured such that they're not a grab-bag with arbitrary gates based on a single universal action; I think there should be breadth and depth of choice as it pertains to which powers you get for what reason. Basically, I don't want feeding to be the only way to unlock new abilities and I think existing abilities need to be reworked to be more situational rather than broad utility that's used by everyone and their mother. I'd also like to see vampire go from being vampire and more of an all-encompassing supernatural. Basically, I'd like for there to be choices aside from playing the most obvious vampire archetypes, or at least make those abilities and archetypes more mechanically interesting.
I think these choices would allow for more personal freedom in gimmicks and incentivize roleplay over strict mechanics. Part of the appeal of gamemodes like Traitor and Mercenary are that they're incredibly free-form and let you do literally anything and trade for whatever the magical shopping cart doesn't have, and relatively recently have received psionic starters and such inside the uplink to allow for even more creativity to blossom (with discussions regarding changeling and vampire starters having been made as well, though I forget their consensus- either way, I support those too for the same reasons). The more options a "vampire" has, and the more people who can execute unique ideas there are, the better.
Likewise, please compensate IPCs and Diona. I don't like readying up, as an antagonist or otherwise, to be completely stonewalled each round because of silicode preventing the clean inclusion of it. I would really like to see IPCs and Diona be given the ability to bite and drink blood, and then the players allowed to flavor it however the hell they want. These two in particular (unorthodox mechanical species + the literal blood-drinking species in canon) would be amazing to have on the roster, and if unique abilities for them were implemented, all the better. (Imagine a more potent Diona bite that forces your character into an emotional state? An IPC that runs off of blood and can meld it with its steel to create weird fucked up blood-metal-alloy weapons, or turn humans into biomechanical thralls from some kind of fucked up virus? Stuff like that.)
As a non-antagonist, as it pertains to one of my previous suggestions I would really rather there be other abilities or items than combat and escape tools. As it stands, some of my worst memories of any antagonist come from them and changelings—I don't speak for everyone, but I can say that "I'm going to be bloodthirsty and then frenzy about an hour in" is something that's been seen a frustratingly disproportionate amount of times over the years. I believe this is due to the constraints of the extremely combat-oriented abilities with absolutely nothing else (not even an uplink or access to exploitables) to compense. I can't remember the last time, if any, that a vampire round held a genuine narrative and wasn't just "my character is a vampire now", "give me bloodpacks or die", or "I'm going to frenzy 40 minutes in".
As both, I want to see more narrative options that might or might not be strictly aligned to the "vampire" theme. Let me or others do weird freak cult (the generic kind, not the Nar'sien one. Although...) nonsense, be some demon from hell, a half-dead geist, a fey-touched weirdo, or other mystical bullshit. Revenant (the gamemode) plays to the supernatural themes but never gets voted and is incredibly antiquated because of its lack of round-start antagonists (instead spawning them in via ghost role) and general lack of fun without adminbus. To those ends, the more weird magical nonsense you can do, the better. Besides, what other gamemode implements magic, the unnatural, or religious as core themes? It's only cult, and I want more variety than that. It would allow for more bizarre and "out there" gimmicks that break the mold and flip the setting on its head (like cult).
Astute observers may notice all of the supernaturals I mentioned (demon, geist, "fey-touched" being a replacement for another that I'll explain in a sec) are references to White Wolf/Paradox Interactive, the same people who made Vampire: The Masquerade. All of the weird, cryptic, gothic stuff they have in their books is fucking delicious as fluff and lore. Obviously at a point what's being added far exceeds the original scope of "just make the Vampire mode more Vampire", but I can't but attest to the idea of getting more gritty mechanics or flavor items as it pertains to what would basically be Aurora's Demon: The Descent, Geist: The Sin-Eaters, Changeling: The Lost, etc. It would just be cool as hell from a variety and narrative standpoint; at least for vampire specifically, I think the massive amount of stuff you can either import or take inspiration from as it pertains to White Wolf would offer an insane amount of variety while retaining the intrigue-heavy roots of vampires in fiction. Bonus points if you do anything with Exalted.
I could talk at length about their abilities and how to implement them, but the long short of it is look into V:TM's "Disciplines" and then work your way around the rest of the books. Changeling: The Lost, for instance, has Contracts instead of Disciplines, which are still magical effects they can enact at will. Exalted has Charms. etc etc
Anywho: TL;DR I'd like more abilities for variety and flavor, reworks of existing combat abilities OR additional abilities that are strictly non-combat, to see IPCs and Diona compensated or included in some way, and the supernatural part of vampire to be the most touched on rather than the idea of vampire existing as solely vampires. The reason the other gamemodes are popular is because they're very free-form and offer a lot more than meets the eye. Pretty please, give me more supernatural stuff to play with- I can easily and very happily imagine a world where people vote Mercenary for canon-derived gimmicks whereas they'd vote Vampire (or Supernatural etc.) for otherworldly, bizarre, or mind-fucky stuff.