#1 - July 16, 2011, 7:53 p.m.
Just make the Real-ID friends of the party leader appear as though they are a member of the party-leader's faction to avoid damaging immersion for others present, just like you do in CoT.
Ultimately, you're already going to the considerable trouble of getting this service off the ground; it can't be much more of a headache to make it work cross-faction. I'd happily pay for it if you did this.