Actually I wanted to try an Eberron campaign. IIRC it doesn't come out until sometime in June or July, and I would need at least a month or two before learning the campaign world. So I was thinking August would be the earliest, and that was before someone else wanted to try DMing. I don't have any problem with waiting until someone else's game is over. I had actually considered doing the Eberron game a low-magic version because we kind of needed one after the sorcerous might of the Coldfire campaign, but someone else wanting to DM a low-magic game is even better 1) because I can be a PC, and 2) the Eberron game can be high-fantasy like its supposed to be.
My brother really likes the superhero Modern campaign, and I think everyone else is liking it so I doubt we want to end that one anytime soon. My camaign was built with a very specific story to it. At this point I have laid in all the clues and hints to figure out what's really been going on. All that's left is simply to put all the pieces together and find out what the surprise ending is. It could easily be finished in one session just depending on what the PCs do. With the evil game sort of on the backburner most of the time, its seemed to work pretty good. More than three games at once and I think we could start running into problems. Also if we ended my game sooner, we could probably fit in a few more sessions of the evil "Anniaserean" campaign which would be fine with me since there is so much I want to do with that character.
One thing I've liked most about having more than one campaign is I generally like campaigns that last longer, but there's also a lot of characters I've wanted to try out for a long time that I've never got a chance to. So with having more than a single game I've been able to try out multiple characters without having each campaign only last a handful of sessions.