As previously discussed, I'm considering running a sequel to a campaign I ran a few years ago as this year's summer game. I haven't fully committed to it (and likely won't until late April) but it's one of the possibilities I've been turning over in my mind.
The idea presents some significant advantages. First and foremost, I'd get a huge level of buy-in from my two most active players, who have wanted me to run this ever since the first campaign ended. A secondary consideration to that is that this may be the last time for a while that one of them is here for the summer, so this summer may be my last chance to do this. On a different note, I've been thinking about running d20 again for a while now, and Arcana Evolved in particular is a ruleset I'd like to go back to.
Leaving aside outright disadvantages (i.e., the campaign might implode under the weight of player expectation) which I've given careful and sufficient thought to, the campaign also presents some significant challenges. One of the reason the players are interested in the idea is that they'd like to play, at least briefly, their old characters at high level. The last campaign ended around 10th level, and there's been a sufficient span of time in between to more than justify them now being 15th, or even 20th level. However, for various reasons those characters are now largely restricted to the city that they dredged up from the bottom of the ocean: in addition to some mystical business with an NPC they're strongly involved with, they're trying to found their own country/empire/thing, and managing and defending it keeps them busy.
I don't want to run "let's defend this crazy city." Not exclusively, anyway. I think that game could be interesting for a while, but the group has enough power there that I want to be able to force them out of it occasionally, to go deal with some problem or another that's still relevant to the city, but outside the range of their various massive advantages. I've considered putting a weird underground complex of some kind underneath the city, for exploration and as a source of danger, but I don't think it's a particularly good fit for the ruleset, and I don't think it can fully support the rest of the ideas I have in mind.
Oh, and I also don't want to have to deal with high level characters all the time. Even if their capabilities prove more interesting than frustrating, I don't want to be wedded to the math, and the attendent hours-long combats. I'm curious about what such a game would be like, but I've heard enough about it to be wary.
The rather obvious solution to all this is to give the players each at least one additional character, lower in level than the original group and likely tied to the main characters in some way. Create a group of lieutenants, essentially, as a strike team to handle any off-island problems that may arise, and to deal with things that the main group just doesn't have time for. Furthermore, if this secondary group are really the main actors in the game, with the old characters coming on for occasional cameos, I have a lot more freedom to add new players to the game, which I'll probably have to do. Much more reasonable to add a new lieutenant than a new 20th level master of the city. (Though I have some ideas in that area, if it comes to that.)
To make things more interesting, I'm considering a twist: each player has to run the protege of a different character. So if, say, a long-lost illegitimate kid of Blank's shows up, Blank's player doesn't run him and the kid. Someone else runs the kid, and then they can have heartfelt family conversations without descending into schizophrenia.
I like this idea, since I think it'll mix things up a bit, but my players may have other ideas. I still haven't ironed out the details yet; still need to figure out how involved the old characters will really be, and I haven't ruled out true troupe play, with more than just two characters per player. (Especially as my current scheme will leave the new players who will undoubtedly join the campaign with just one character. Maybe I'll figure out something special for them.) For the most part, though, I'm trying to avoid any too serious planning until closer to launch time, in the hopes that I won't lose all interest in the idea before then.