It would be amazing if the personas/demons had different styles depending on the game they are in. It could give the non-Kaneko artists a chance to shine (or fail miserably).
I hope Persona 4's success allows them to do this. It is a big opportunity to stand out from the crowd.
I don't think I'd want any artists outside of Kaneko, Soejima and Doi to work on the Persona games. The guest artists in SMT4 were awful.