Please post below if you'd like acknowledgement on this thread from Bethesda, or in the very least, this could be a solid place for the developers to see what the community wants are, all in one place and hopefully incorporate or take ideas in their building of future DLC.
The forum rules clearly state that petitions are not allowed on the forums.
At this point I don't think we need a centralized location for all DLC discussion. As for collecting information, Bethesda devs view the forums frequently and I'd say they've well demonstrated that they listen to fan requests when making DLC.
Tribunal: added pack animals, a hireable companion, and much larger and more involved dungeons
Bloodmoon: more traditional landscape, ability to built (and direct) a settlement, werewolves
Shivering Isles: more bizarre landscape, more involved player choices
Broken Steel: extended main quest, made it open-ended
These are all major features, a lot of smaller things also seemed inspired by fan requests.