All religions, wonders and corps prebuilt in an inaccessible city. (=no contact with that civ for anyone!)
No religions would spice up diplo for sure. Happiness would be tough too.
Objective: Win any peaceful VC

(= culture, space or score)
Other restriction ideas for the same objective:
- no happy resources on the whole map, hereditary rule banned. (This could be very tough!)
- maximum 6 cities can be owned by the player - pretty standard game
- some crazy maptype
->> all tiles are strategic resources on grassland
->> no strat resources until astro, they are placed on 1-tile islands in secluded places
->> Deity, 3 continents connected on 1 tile, the place where our settler starts. One continent is unhappy, one is unhealthy, one is unstartegic. They only have the corresponding resources, so no strat resources for the unstartegic, etc. Could be the same but with 4 islands, our island (which has no resources BTW) have galley acces to each, but they don't have access to each other (some well placed mountains are needed of course). The AIs could get extra good starting positions to balance the restrictions.