I would not try the approach of a single map that is trying to suit to everything we want to do. That can potentionally end up with a map that is "okay" at everything.

It is a bit of a shame that rivers and ponds are not working that well (or not at all) in ArmA 3. But I think something we have avaible at the moment would a terrain that also offers some gameplay for boats. Just imagine something like this in ArmA 3.

Would be pretty nice have a map where a big part is river delta with some nearby vegetation including small villages and maybe 1-2 a bit more larger villages.