I've said it before and I'll say it again - If Valve are going to add any new gamemode, it has to have more than one official map to support it. 'Territory Control', 'Medieval' and 'Special Delivery' modes all deserve a couple more official maps each. I don't count the Halloween version of Doomsday in this as iIt's just a re-skin of an existing map.
Just because those gamemodes aren't popular doesn't mean there aren't people who enjoy playing them, and even they get bored playing the same old map time and again.