I have like a zillion ideas I didn't go through with (yet, anyway)

I planned an RP in renaissance/post-medieval Europe wherein the many superstitions of the lands such as werewolves, vampries, witches, the loch ness monster, chicken-footed houses, basilisks, daemons, banshees, etc. are all real. But I thought there's not enough of a crossover of people who are interested in history and supernatural shit to make me get a nice audience.

I wanted a Fallout RP set in the massive OWB Mod setting, but I struggled to somehow think of a way to bring all the content I wanted to show from Mexico the land of Titans to the Northern land of God and Cannibals. Perhaps some sort of copy of the cancelled fallout tactics story except less silly.

More whacky, I wanted an RP where people can sort of let out their inner power fantasy from all the edgy books and dusty 90s/00s animes out there of intergalactic barbarians and knights and wizards and prophecies. It was to be very lighthearted of course, players more or less givne free rein to one-up their enemies in B-movie tier twists where you reveal some hidden power. Just cheesy nonsense

I also wanted to do a more grim RP in the world wars. For WW1 like some KuK conscripts that hardly know each other's language desperate to not get pummeled at the Isonzo by artillery or on the East beheaded by Cossacks, or if the second world war then follow some Tommies on their road to drive the fascists from France.  

On an ending light hearted note I thought of some absurdist RPs. Either an arena style battle royale where players are dropped in a walmart and must slaughter each other with its contents, or alternatively chronicle Florida/Polish/Brazilian men as they have a huge acid trip. Also perhaps a joke/meta RP chronicling the more memetastic eras of RPG personifying the free section as a crossover of a huge kingdom and an anime convention, the advanced section as some sort of snobby country club believing itself to be a great nation unto itself, etc.