no one knows for sure right now. patch and expansion are only out a couple of hours.
I'm sure though that chuy will make a statement on this issue as soon as he has gotten some info from EA on the implementation of the SF stats into the current xml stats feed.
my personal opinion would be that as you are going to use the same account for SF as for BF2, and weapon categories are the same, there will be no separate stats from EA for the expansion. It will all go in your account and you will have no means to differentiate between stats earned in BF2 and those earned in SF.
On the other hand, we already know that the unlocks requirements in SF are different from those in BF2. Accordingly, there will have to be a separate recording system / display system for those.
also, stats for the new maps will of course have to be displayed separately.
Am I making sense ? No ?
Probably because I am just guessing here.