A time-traveling RPG Action Adventure, Larger than Skyrim Open-World(s), Completionist-like with 1200 hours of side-quests/collectibles/unlockable artwork (like the old days with Mortal Kombat's sketches, mokap pics) but I'll never be able to. I can barely follow instructions to hack.
I think I'd make an RPG that changes course depending on the choices you make, kind of like Mass Effect.
The only problem is that designing all the possible endings must be a pain both for the programmer and the artist.
a multiplayer board game (cards game), puzzle game (picross API client), or a topdown adventure game (zelda, summon night, etc.)
never had time to do either, it will probably stay as an idea only seeing how much time I spend coding homebrew.
My dream game that I've always pretended to be making is a 16-bit style rpg featuring my writing and poetry. I've actually started making this several times...using different versions of RPG Maker. Sadly, I must say that "Poesia: Power Of The Verse" will never be anything more than several minutes of introduction and some very limited PoC game play... (I did start converting it from Ace to MV recently, but...yeah, probably never gonna be finished due to my lack of map-making and graphic design abilities)
If I could get my hands on the IPs and if I had the skills, help make another Advance Wars and Custom Robo game.
Generally, a open world game like Skyrim with magic set in the future, like Final Fantasy or Shadowrun. Just to defy the medieval fantasy trope. Also, optional local and online multiplayer.