I think the only problem would be is making sure your guest stars can 'guest' seeing as they'd probably join the RP if they could so you'd have to make sure they were free for the allotted time you need them for. Plus, let them know approximately how long they'd be in for.
I am curious, how are you going to find the guest stars? Are they going to "sign up" in the OOC like everyone else? How would that work?
The 'guest stars' wouldn't be signing-up in the most traditional sense. When the RP gets near a point to needing the first batch of bosses(I'll usually try to keep it in grouping of 2-4.) I'll make a post in the OOC topic about looking for some antagonists....and also in that "Roleplayers Wanted!" topic. Applicants send a PM instead of posting in the topic to keep things hush hush and not ruin the surprise. From there it's gather the list of responders, make selections, send out PM's asking if they're able, hand out individual boss characters and we're in business. If the list runs dry due to using up all the people on it who keep interest then it's just a case of rinse and repeat.
My only concern would be is that I hope that people don't just go "well, I'll just be a guest star instead of joining" because it's less work, less commitment, etc. Then you'd get less roleplayers because they'd rather do short-term than long-term work.
Yes, I also see this as a flaw, so one of my planned actions is to not mention the 'guests' on the OOC topic until applications are needed. Though to be completely honest, I would love to PM just random RPers from the community and ask instead of somewhat ruining the surprise by declaring that there will be special boss RPers...at least for the first few bosses, since it would become routine afterwards. Hell, I actually had reservations about even asking since it would mean any potential 'main cast' paying attention to this topic currently now knows the surprise and hopefully won't ruin the fun. I'm just not sure how effective getting a PM from someone randomly who has been inactive for about a year will be.
But perhaps the "real players" could also choose to only participate in some chapters? Like, maybe they were in the first chapter, then not in the next, and then in the third again. Something like Venice (I think?) where you can sign up for chapters/arcs.
Or, you can just recruit your friends here to be the guest stars and keep the "real players" as proper members of a RP.
Eh, that really wouldn't fit the theme of the RP. It's meant to be sort of team based, and not segmented into chapters or sidestories. If there's enough players though, the team would be able to split up, with group A taking on level X and group B taking on level Y, but would be simultaneous and still follow the traditional RP format of continual activity. The thing I'm tinkering with isn't meant to be integral to the RP, just some side fun to our regularly scheduled programming.
But now you've reminded me that I have no friends(on here at least) and the ones I did have been inactive for years. :P
Has anyone really been far even as decided to use even go want to do look more like?