Glad I am not the only person who thinks she Rochelle is a irritating bitch
You're new to the forums aren't you? She is completely despised by everyone, she was so bad that they've actually re-voiced her with new lines, however players still find her unbelievably annoying. We just want her to die so we can find another person.

I'm pretty sure Valve will let you play as them. Maybe not as easily as "DOWNLOAD & YOU GET THEM!". You might have to unlock them or something. Valve isn't stupid, they know we want to play as the old survivors.
Sorry to be the bearer of bad news, but VALVE already announced that they will not be playable, and for that the design team will be damned to the deepest circles of hell.

What about copying the audio from L4D1 to L4D2 for the Survivors with the skins, eh?
Then there would be an unbelievable lack of audio because most of the audio comes from interacting with the environment and the particular original levels, so the only ones that could be properly transferred are things like death screams, incap yells, etc. They would need to re-voice things to make it viable.