As far as i know, the game mode of the next contest is already set, but we will only know it when it starts
And believe me, 5cp isnt that easy to balance, i have already nearly 10 versions of demolition tested, and its still not finished (though it was my first really planned map).
There is already a community project like you mentioned, must be somewhere in the forum.
really? What is it?
Im gona start making a map RIGHT NOW!
Just plain old CTF map contest.
Actually do-able for people with tight schedules and it even ahs the chance to be played by the non mappers community/ more likely to be endorsed by valave.
IMO it was a bit foolish having the A/D CTF contest, all those people put so much work into maps that most likely won't even be played again.
KOTH and Arena are, however, the most abundant customs because they're so small and relatively easy to make.
I'd suggest a one-stage attack/defend CP map, like Gravelpit - but also like Steel.