I would like to see a challenge with a timer like the ones in the campaign. As in, a countdown timer. You must eliminate all enemy AIs within 30-90 minutes, depending on the size of the map. Say, 30 minutes for a 2P map, 60 minutes for a 4P map variant of this type of challenge, and 90 minutes for a variant of this challenge on an 8P map.
"There is no greater Void than the one between your ears." - Void Ray, StarCraft 2.
Especially the Void between the ears of people who think that No VTOL is a good idea, and won't lead to arty wars. I've won one, and I have to say: I hated it.