I have though a little more deeper on the subject after this thread has been created.
For me, the only important thing is the one character for poster rule, that I would specify as the following:
"In the missions can partecipate just one character for each posting user"
I don't mind if Tobias or anyone stays with Vanguard, and if Laslie is an active member as Phil. Just, on the missions, i.e. in the main body of the story, each poster should bring just one character, for the reasons TTT has stated perfectly.
About Grissom, I prefer him, as an Oracle type, than a made up new character. We know who he is, how he behave, it's better than to have a new person, IMO. Plus, we can always hope to have Chewy writing something, even if sparingly.
The only touch I would like to see added, is something to explain why he has stepped back from active roles, like a temporarly incapacity of any nature (illnes, legal, or anything else).
That said, I still think that Pro's idea for a story is great, and if we could use the characters without (for now) posters (lance, TC and NotWedge) for that, I would be veary happy.
