Conquest could be really fun if you where to be able to mod into something like a 'push' game type. But it needs good linear maps and fixed spawns
CTF, great game mode, no good maps for it. Been working on some but the map editor is a pain and balance is hard. You need to give cav a role, but yet not make it dominate. Same with archers and inf. You cant copy a classic CTF map (like 2 fort) as in those games all classes have ranged weapons. Something you dont have in WB. And fix the spawns =/
And lastly siege, well i am ZHG what can i say

we like siege. (and TDM)
ZHG has 2 ZHG events a week. (mondays and fridays) where we sometimes switch over to less played game modes. CTF stays populated the longest of them.