I was thinkin about the polls (like townscreen-petition,...) and then I got the followin idea:
As to get a feedback from ALL fans, you could give every1 the opportunity to give a feedback about the game who actually bought Heroes VI.
e.g.: 2 weeks after the game was installed, the player will be automatically asked to give a feedback which will be send to UBI. (via the game itself or by sendin an email or....)
The point is that UBI gets an impression of what every1 wants. (Not just of this or that forum/single fan/...)
That would also make it easier to correct and find bugs & faction-ballance problems. In addition, if there are things that almost every player absolutely dislikes or (on the other hand) wants to be changed then UBI would have it in black and white. (: