Agreed. I would also add that if you do an XP incentive, it could be per character on the team, with a cap. Like 2-3% per team member, to encourage groups. If you have it "swap back" it should only do so once the imbalance is >15% or something so it's not like a see-saw. Further, the buff should have a 1 hr timer and refresh if the conditions are met. That way you don't form a group on the lower population side and then have your buff yanked away after 5 minutes.
Actually I agree with you. Alternatively I also wouldn't mind restricting (some) powersets or offering hero/villain variants of powersets. But at this point I don't think anything like that is ever going to materialize, for a number of reasons. Villains are heroes are villains.
I like this suggestion as well! Though I don't think this will change things much, I still like it conceptually.
Honestly I feel like Null just exacerbates the issue. Not enough villains? Join blueside and reduce redside population further! Uh, did that fix the problem yet??!? ADD MORE GULLS! It's well-intentioned but it doesn't address the imbalance. Gull should be used to help people play a particular character (which they feel like playing or fits a role needed) with whichever side their buddies are on at the moment, rather than as some sort of population imbalance panacea. Might as well just delete redside.
