1) Asymmetric RTS / FPS. A group of FPS players play through a map against an RTS player who is controlling the tech, types and grouping of mobs, etc.
2) RTS / FP coop game sort of like Warcraft 3 where one player controls the base from an RTS view and another player(s) control a hero and a support army.
I don't enjoy MOBA's but they are super popular. I love Starcraft but it is too hard to get into. Takes tons of time and effort to get the basics of 'how to play'.
3) I think a game somewhere between Starcraft and LOL would be interesting. Clearly it is all about the details here and I don't have them - but I think you could capture a really big gaming market by trying to simplify the macro of Starcraft, keep the micro, army movement, base building, expanding etc. Controlling and upgrading lanes of a moba map?
I have no idea how any of these would really work out from a game development point of view but I think they have potential to be a lot of fun and bring some new life into the RTS world.