I just thought of something I think would be completely amazing.
What if there was a MOBA (DOTA, LoL, etc) mode for TF2? Think MvM, except like a Moba, there'd be something to defend and there would be bots spawned periodically from each team, the thing that would be neat is that there could be the upgrade type thing from MvM (tuned down a lot obviously, otherwise it'd be just a tad crazy). Players could get for example $10 for killing a bot and $100 for killing another player. I don't like MoBAs all that much but this sounds like it'd be amazing.
To fully grasp what I'm saying assuming you don't know what a MoBA is, play something like LoL (League of Legends) or DOTA 2.
Something like this would be completely crazy and i feel like I'd enjoy every second of it.