If it were possible ( I don't know whether it is or not) it would be amazing. How would it work though? Would you be part of the same party?
If so then who would move you around the map?
If you moved separate avatars what if someone got into a fight, what the other person do?
Would they sit and wait in a spectator mode?
If thats the case then how would two people get to be in the same battle without facing each-other?
Unless it was a totally different system where you travelled about in real time which would solve some of these problems, but would add a tonne more problems to the mix.