I've done this for the first time (well, half-done this) where I basically made players follow a certain theme for the team they'd be on in the IC. I can tell from the lessons I learned from that that this is something I will do in the future as well (and possible double down, pre-selecting themes I want to see and/or character types). 

One thing I worry about is that, with certain niché RP's, you might force people a certain way that they don't want to go in and thus diminish the already small playerbase. Could be (easily) offset by just having smaller invite-only RP's, but people don't seem to like those.