Things I'd love to see:
World:
Low fantasy, like Warhammer or GRRM's Song of Ice and Fire. Minimal magic, maximal amount of grittiness and backstabbing. The system should also reflect this (e.g. warriors shouldn't be able to shoot shockwaves out of their weapons or become invincible for a short time; the combat should be fast and lethal, thus encouraging the player to try to resolve problems differently).
HIgh-magic dark fantasy: magic shouldn't be available to all, but it should play a huge role in shaping the world. Some Lovecraftian feel would also be appreciated. It is also entirely possible that in such world magic is considered to be capable of causing harm only.
Anything based on the tabletop systems of: new World of Darkness (especially Changeling: the Lost), Dark Sun, Ravenloft, Planescape, Warhammer 40k Dark Heresy (or anything 40k really, except Deathwatch), Kult. Though I'd like to see my money go toward directly the development process, not licencing.
A somewhat Planescape-like world based on ancient Greece... I've always thought Plato's "Theory of Forms" would be a great theme for a videogame. A world where there are no gods or magic, but there are ideals, and one could gain more and more power by striving toward one (although thus shredding away more and more of his humanity), becoming capable of warping reality in accordance with said ideal.
System:
I don't believe in levelling up, instead I think the players should be able to spend their experience freely along the way as they see fit (to attributes, skills or special training - like spells and combat moves). The problem with game balance should also not be an issue, since there could be a 'minimal xp spent' level until the higher-tier abilities become unlocked, or there could be specific events ( e.g. training, choosing certain ways to resolve situations etc.) regulating what the player can and can not pick up.
I also think "health points" are a good thing if you want a balanced and tried system, but developers should experiment more. I'd try a somewhat Deus Ex-like formula where there are no hit points, but hit locations and severity of injuries (no damage for the weapons either, but a chance to cause injuries of certain severity - this could be modified by the successes gained on the attack roll, and the wielder's strength). It could be an entirely valid option on higher difficulties for the character to become crippled, lose a hand, etc. Of course, this works best in a grim and gritty world, otherwise it's quite pointless.
And finally... in the world of VOd characters, there is a tendency for the main character to be more than a vessel, an avatar for a player, and develop an independent personality. In the world of tabletop RPGs, it was always a natural assumption that the characters have personalities, so I don't think it's a problem. On the contrary, I think the industry should embrace the idea, even utilize multiple main characters (where the player could not choose alignment or personality for his characters, but attitudes toward certain topics and persons; and the game should remember those choices, and when said character's not controlled by the player, it should behave accordingly). This would create possibilities in elastic storytelling which put even Alpha Protocol to shame. In an intrigue-rich world it could be a great thing (but otherwise it would just needlessly complicate things, or not have any impact on the actual gameplay - then what's the point?).
In general:
Actually, I'd love to see anything from you guys. You've never let us down. (I sincerely hope though that said "anything" will involve something very-very PST-like).