What about you Rabbity_Thing?
My three votes were for Renaissance, Industrial Revolution and Cyberpunk, though truth be told coming up with the poll stimulated my imagination and I had very compelling ideas for RPGs in most of the time periods.
Renaissance would make for a fantastic base for an RPG setting since the shape the period took was a mix of influences from medieval era that preceded it and a newfound fascination with the legacy of (Roman) antiquity. I could imagine a game set in a tumultuous region of wealthy city states crammed between mighty empires striving for influence and balancing on the brink of open war. PC would chose his city of origin and social background and be thrust into a world of scheming and intrigue, his adventures would take him from seedy underbelly of his home through gruesome battlefields and all the way to palaces of doges and dukes trying to outcompete each other in both patroning grandiose art and backstabbing. Marble columns, zweihanders and gaudy hats.
Industrial Revolution because Arcanum. I could elaborate and share my own ideas, but what for? That game played it's hand masterfully when it comes to the setting. I'd like to see some RPG very much in that spirit and if I'll ever get it, I'll take it from there.
Certain recent release from cyberpunk genre felt like a spit in the face, especially given how I hoped, despite all good reason, that it might be the one to fill the Deus-Ex-shaped void in my heart. Tropes of the genre are rather well known and require no elaboration, so all I'd like is to have them incorporated well into a grim, noir-y RPG with good deal of attention devoted to storytelling and C&C.
There are others, like the Prehistoric setting where the story would depict PC rise (or fall) within his tribe living in magical wilderness with spirits and old gods and primordial beasts rife with tribal conflicts, feuding deities, shamanic magic and perhaps a Kurtz-like character that would force the PC to unite the tribes/make a valiant last stand/attempt migration to avoid enslavement/abandon his tribe altogether - each of those paths shaped by decisions made in the past, with friends to call upon or vengeful rivals to confront. In my mind such an RPG would require completely new idea for itemization - one stone-tipped spear wouldn't be much better than another and there would be no master craftsmen to create legendary armors. Maybe gathering magical ingredients from powerful beasts, rare flora or as a reward from magical beings and then using them to craft shamanic runes that would grant buffs or modifiers? Haven't really thought it through enough to make a pitch, just throwing this idea around.
And so on, and so on... This brainstorming made me realize that good ideas are cheap. Someone skilled, determined and dedicated enough to bring them to life - that's where true value lies. Such people however need to eat like the rest of us, so they work for corpos churning out bland, imitative shit day in and day out. Fuck this bullshit.