Something that would fix so many problems that people complain about can be easily solved with variable map sizes.
Variable map sizes would allow for maps to be shorter, thinner, wider, longer. This would force the players to think more intuitively about their weapon choices and allow weapons to fill a more specific role.
Right now we have a one-size-fits-all type of map. Maps like Pinpoint, Island, Bridgewars and Normandy have to fill in mostly redundant space by flooding it with water and empty space. Rather than fighting and construction players often spend 2-3 minutes wading through water, trying to get over towards the intel, rather than pushing through the terrain with their team.
The new map sizes would make an improvement to all aspects of this game. Tiny maps for 4v4 (or whatever) would encourage the use of shotguns and SMGs, alienating rifles. While large ones would encourage Rifles and SMGs.
Because of this, SMGs can be tweaked to a more medium range, shotguns to extremely close and rifles to long.
Map quality might be improved, with map creators spending less time filling in useless space with even more useless junk and more time fleshing out buildings and structures that matter.
As far as the mechanics behind this go, I'm not sure. But Ben seems competent enough to facilitate this improvement.
TL;DR
Adjustable dimensions for the map. Would encourage more thoughtful gameplay.
Oh, and I couldn't see this had been posted recently. I'm sorry if it has.