Here are two server ideas I had:
1: A semi-realistic, semi-literate flood RP. As in no superpowers, no summoning planes from thin air, no living through everything. People would get a few moments to build, then the flood would start. There could be several islands/hills scattered about the map so when the water got too high up, you wouldn't be stuck, you could make a boat and drive over to the islands. The issue would be it'd get boring after a while, so maybe there could be something the players would have to do to stop the flood? In my old flood RPs in the Creek map, the way to stop the flood would be to get to a certain spot and "unplug" a hole in the ground like a bathtub drain, which was somewhat unrealistic but pretty fun.
2: A race/obstacle course. There would be a long track that you have to run through with obstacles like landmines and hurdles and such, but also power ups that could give you jets for a few seconds or launch you ahead. The first person to get to the end wins. Possibly there could be a time limit or a board with the winner's names.
I'll try to think of more, but just post whether or not you would join either of these servers if I made them, and if you think something would need to be tweaked or added mention that as well.