I would not be focusing on completely new features but instead work on fixing issues/bugs with what currently is available, otherwise the minor but very annoying issues will just continue to be pushed back.
So far it seems that there's always been more modes added, for then those to fade out or need a lot of bug fixing that takes time away from everything else.
In Order of Importance:
- improving existing gamemodes (Battle, Siege, DTV, Rageball...)
- improving Strategus battles
- bug fixing/polishing (voice chat, interface...
- adding new gamemodes (Stronghold, CTF, Conquest, Commander Battle...)
- adding more depth to combat (new mechanics, stamina...)
- improving graphics (models, textures...)
- changing/improving reward (XP/gold) system
- changing/improving upkeep system
I would say that more depth to combat would be great, I'd be all for that, but it would truly change the face of the battlefield, maybe for the much better, but even so such big changes should happen when the other more regular issues have been fixed. IMHO.
Otherwise
I still recommend mixing some of the Stronghold features in with Strategus (building your own fief etc).
Changing and improving the upkeep/XP-gold system requires some new ideas, so far there's never been any proper ones suggested - at all -
ever, hence their positions as last on my list.
Conquest mode would be great, could even replace Siege perhaps. Otherwise a 'Domination Mode' would be great, something where you had to hold (an) area(s) in order to get multiplier, it should drive people to group up and attack/defend in teams.
Also add Siege/Engineer features, ability to plant a pike in the ground, build a fence, etc etc.