There's one big issue with client possession that I have noticed.
Clients cannot:
-Speak while possessing.
-cast a possessed target's "modded" disciplines though they can cast possessed target's original game disciplines (Feed, Blood Healing, Potence, ect). I have not tested whether the Wodal disciplines can be accessed by a client possessing another target, but noticed that in E-Mod 1.8, none of the possessed target's disciplines will appear for clients.
-leave the level while possessing a target.
The above are hard-coded limitations of the game. I can't do anything about those.