Why do I get the feeling that Rapturous Depth might end up being an actual PATCA mission with potentially party wide results?
I mean, I might as well list in order the people who might end up intending to stay! Elizabeth, Muon (from what AB tells me) for starters...
EDIT: As for rewards, may I suggest for slayers new accessories that are unlocked for all other slayers? Basically, instead of finding just one new item for that PC or so, the adventurer finds something which the scientists back at Ricewood can innovate to create a new invention. It also works better than just improving a single weapon (as suggested above with the "improved dragon slave") because then it would limit the uses of other elements which become lower in power and thus less desirable to bring along.
Am uncertain what could be offered for Trainers/Snaggers or Pokebrids that would not have to be decided on case by case basis. It might be easier to see what rewards are appropriate after some more missions have been completed and we see what the difficulty is like after the new rules.
Additionally, for all the classes, once a certain number of later missions have been completed, access to carry one
Wonder Launcher exclusive item per PC per mission. Great to use for a really tight spot! I dunno though. They are pretty powerful, but it's a one-shot thing.