The ability to create & upload custom terrains for the old H2H was a huge draw for me & others. With the current terrain system, all kinds of beautiful & exotic terrains could be used if we get the same ability to do so with the next generation H2H on the way.
My idea is to be able to upload the custom terrain to the server when hosting a "room" and then when the host shuts down the room, the terrain is cleared of the server's cache, so there would not be a buildup of 100 custom terrains clogging the system. A custom terrain would be in essence "Renting" a space on the server while a player is hosting it & then gone when the host shuts it down. I haven't really asked for anything over the years, but this is the one thing that I really want. Memories of hosting terrains in the old H2H has been the biggest factor in keeping me lurking around here for the last year, when HT first mentioned bringing H2H back in a Wishlist thread.
MA & most SEA terrains are not designed for an 8-32 player arena. As an AvA staffer, it's my "job" to design & run setups for about the same size crowd on the terrains we have now, and I can tell you it's not easy for us to do over & over. I don't want to see the private servers' hosts going through the same dilemma every time they want to run something. My plan if we get to upload custom terrains is to devote most of my AH time to putting out a large amount of 64x64 mile terrains for H2H use by the community. I'm sure many others would also.
That's my wish.

EDIT: May I present Example A:
http://bbs.hitechcreations.com/smf/index.php/topic,313189.0.html