Ever since they were introduced, I think that Horde factions have really been a weak link in TW; they are IMO the least fun to play as and the most annoying in their effects on the Campaign (leaving desolate ruins and wildly swinging between steamrolling and dying out).
I think that it's high time that Nomadic factions were rethought by CA. The implementation of the Vampire Pirates in Warhammer was a step in the right direction by CA. However for historical games, this is still not a proper representation of nomadic empires and how they operated.
From what I have been able to gather (especially on how the Mongols operated), the following would be ideal for Horde factions:-
1. Dependence on the hordes or at least mobile "tribes" for recruitment and replenishment. A horde can only recruit from these mobile bases, and can not recruit anywhere else.
2. Almost complete dependence on conquered settled areas for their Economy.
3. Settled areas would be almost defenseless without the nomadic armies, with little to nothing in the way of garrisons.
4. Hordes themselves could be separated from "tribes". So the loss of an army doesn't crush the faction so utterly. Instead, tribes could follow hordes and allow for recruitment on the go. The flip side being that the horde armies can't replenish at all when not in the same province/region as a tribe.
What do you think?