I have a few ideas I think would be cool.
Solo and Co-op Raids using different campaign levels, as well as different rewards. For example, a raid somewhere in District 9 and one of the rewards could be a Vault Crate Token, but with a percent chance that is the same for all levels. And for lower levels, offer a percent chance to win, say, bronze fuel cells and silver throwing knives, and the higher levels have a percent chance to win fragments of Core MK 4 through 6.
Another idea could be an Alliance Boss/Stage to fight. For example, survive for 90 seconds fighting increasingly tougher enemies for Cash, Alliance Gems, and various Gear, all of which can hopefully correspond to how far in the game a player is.
Maybe we could also have a Game-wide Boss/Stage to fight. Same deal as Alliance Boss/Stage, but maybe have some sort of negative effect, and it will stay there until the players beat it. But there will probably be people who complain that the negative effect is too harsh.
Edit: after reading Robert’s post, I have another idea: Heroes who give other Heroes immunity to a specific crowd-control effect, or ALL of them. For a certain amount of time, of course. And this is different from Heimlock, Françoise, etc. They cure you of CC effects. I’m talking about NOT being able to get CC’d for a certain amount of time. We could have someone who gives out anti-stagger, or maybe anti-DoT, or anti-movement-reduction, or anti-root, or anti-lift.