I was poking through the sound bites for the characters hoping for a new ring-tone then I found some interesting sound files. They were the L4D character's saying lines exclusive to the L4D maps such as Dead Air and ETC, not just No Mercy. There are arguments with the guy in the church-bell room and theres a line by Zoey where she says "Those planes are heading to the airport..." I'm speculating that there may be possible new screen time in L4D2 with the original L4D cast, if not, this would allow mappers to more-easily port the maps of old to L4D2, models & conversations included! I think it was in Code: steam\steamapps\common\left 4 dead 2\left4dead2_dlc2\sound\player\survivor\voice\* Look for the files that begin with WORLD To be honest, the pessimistic side of me just thinks that they did a full audio dump from L4D to L4D2, never hurts to be optimistic
I think that once the sales start to die down for l4d2, they will merge the two games anyway, bung it on steam for an extorcionate price and make more sales.
I think you may indeed be correct, I was just listening to some of the files and I heard Zoey say something to both Nick and Ellis. So it looks like they might merge after all.