I'm not going to sign up for the exchange because Lily/Severus is one of the few pairings I have very specific ideas about, but I'm more than willing to pinch-hit should someone drop out. If you have need of me or would like more specifics as to what I can write - my email is envinyatar15@yahoo.de :)
If you need someone to help you out with running the exchange I'm there as well; I'm running a smallish exchange myself (20 participants last year, dates nowhere coinciding with your planned schedule), so I have experience with how these things work.
I'm looking forward to a great exchange once it starts posting, even though it's some time until then!