Votable server gametype settings
It would be really awesome to be able to vote gametype (1v1,ctf,ffa,etc), physics (zdoom vs exe), and other currently unvotable settings in player voting. Obviously servers don't have to enable this if they don't want... But you'd get a lot more use out of servers with this, and players could play what they want even if its not hosted outright.
I actually have a design document for 'playlists' on my hard drive, where there are multiple 'categories' of maplists that can be voted between.
However, I would prefer to wait a little while on this, as the console interface in order to implement this would be pretty complicated, not to mention the underlying bits to make this work would require a little reworking.