I'd be inclined to start with:
1) Subscription for more stable ongoing cash flow.
2) An in-game "Kickstarter-Style" launcher with polls:
* Vote on the type(s) of regular patch content you'd most like to see coming up soon.
* SIGN UP for new expansion content you want. See below.
Regarding "SIGN UP" I would suggest, taking housing content ie Hearthfire as an example, there may be several proposals listed that the devs feel are workable. Each would have a per-player price next to it. Content such as this could be unlockable on a per-player basis. A number in the small print below could indicate the TARGET number of players needing to sign up before FULL funding is reached and the current number. A timescale would estimate rough completion time expected. ONCE the target is met, development would begin and players be charged. On completion, those players would automaticaly receive the new content. Others wanting it would have to sign up then, at perhaps slightly higher rates?