I think this is a good idea because I agree that those are the best. The courtesan was my favourite character but she is already on it. I think that the prowler should also be on Revelations. I really do approve this idea.
Small problem with your idea: everyone likes a different character from ACBMP. Even if they chose by some scientific poll which ones are most popular (I doubt it's the pariah or mercenary), there'll be lots of poeple whining it's not THEIR fav. As much as it sounds 'sweet', it is just a wet dream, will never happen.
Am I the only one who noticed that all the people who're enthousiastic about this thread have a join date of maximum 2 months ago? Just to file these new people in: support for both ACB as well as ACR have ended completely. The community tried to get more fixes and requests and in the end, misinterpretation of both resulted in a lot of bad stuff. Also, the development team (who would be responsible for implementing said characters in the game) are NOT active on these forums. Only community members and moderators. These moderators can pass the ideas on, but last time the community tried that it required a boycott.
In short: making threads like these will (unfortunately) result in nothing.
I would love it if they bought back ACB characters into ACR but there are two major issues:
1. They would have to remake all their unique kill animations (except maybe the Reckless kills) to match those of the ACR characters. Just look at what happened to the Courtesan. They would just lose all their individuality.
2. It will most likely be over-priced DLC. As much as I like the ACB characters, I'm not willing to pay (a second time) for characters I've played before.
Ubisoft tried this same idea with the ACB maps, and it wasn't very succesful.