The leveling time isn't a problem for any of the above either; I found a pretty quick job-leveling method involving disabling an enemy, and hosting supervised gladiator-style sparring sessions. Baring that, there's always surrounding a KO-ed foe, reviving them, and KO-ing them again, repeating as long as needed.
Anyway, here's a brief explanation of my thoughts on each option:
a. Add ~4 more active characters to the roster. In exchange, players can't have a pet unless they've taken the Beastmaster skill.
b. We nix level-grinding, and pick combatants from the roster randomly, making combat lethality a bit higher. New characters will be leveled to the party average.
c. Instead of adding waitlisted characters on a first come, first served basis, add them from the list at random.
d. Periodic dropping of inactive/abandoned characters; maximum of 1 per update.
e. At each new chapter the waitlist gets wiped, giving folks a new chance to get a character in.
f. After each chapter, we build a completely new roster of characters.
A. I kinda like this, but it does mean all characters will be getting less screen-time. I'll leave this up to you guys.
B. This would speed things up significantly, but is bound to result in an underleveled roster. I think XP/JP mechanics boost gains for lower-leveled characters to compensate, so they should lag only a few levels behind. I might split folks into 3-4 rounded teams (~3 units each), and randomly pick one team per battle, adding in any additional characters at random. Also, so long as I only bring Ramza into plot fights, people should keep pace once we start roaming the map more.
C. This lets latecomers still have a hope of getting a character in. Alternatively, I could switch between picking the next on the list, and then picking one at random, to keep first-come priority, but still give newbies a chance.
D. I know I do this in other LPs... I'll add a character for a DF succession game or something, and won't check back until I have several updates to read. Since I want to run this more interactively, this helps prune out abandoned characters to give active people more of a shot at getting in.
E. Similar in spirit to C., with a bit of D. and F. as well. It lets latecomers and early followers get an equal shot at getting a high spot on the waitlist. Also, character submission guidelines might change as more classes open up... the style I started with was built around having only Squires/Chemists to pick from, though we now have a lot more options. The strategic role each character will play in combat is rapidly becoming more important.
F. was inspired by the time/situation shift between Chapter 1 and 2 (Side note: I know the plot up to the start of Chapter 2). I like our current crew, and want to keep them around for as long as possible... but the theory was that F. would burn through characters quickly, and give more people a chance to participate in the LP. There's a trade-off.