As someone who constantly tries to take X idea and make it work in Y ruleset, there are a literal ton of games I'd like to see done/do. TO NAME A FEW (or break them down in a non-standard thematic way of 'those should not go together at all')
SPACE!
Star Wars, Eclipse Phase, Spell Jammer, possibly Equinox.
My interest in these relies heavily on getting some flight sim code happening, so the more I will love it and am more likely to play, the more likely everyone else will hate them. RIP.
CRUNCHY!
Mechawarrior/Battletech, Iron Kingdoms RPG, or Pokemon Tabletop United.
Two of these are tabletop wargame settings/rulesets, so all the crunch. Battletech might have gone in space, due to Aerotech, but I'd be down for not having real-time flight for it. Iron Kingdoms, meanwhile, almost requires RPG skirmishes to function using wargame rules, including listing weapon attack ranges in inches, because 'lol, of COURSE they will be using miniatures!' Pokemon... is Pokemon. Game Freak will no longer let you catch them all, but that won't stop us!
TOO TRICKSY/...HOW?!?
Cosmere.
Literally just a mosh pit of the assorted cultures and powahz taken from the various books of the Cosmere. I have put 0 thought into this one.
Probably some others, honestly, but those are the ones that come to mind while being distracted at work.