FISA limits intercept, surveillance, and search, not collection, from what I've read of it (I don't think there is any restriction on collection). They have chosen the (IMO bad) interpretation that merely collecting information is not special at all.

You'd "voluntarily" wave the protection of that collected data, so it would be identical to "give us your last 10 years of email", except conveniently they would be the ones holding it for you.

(I could be wrong; I'm really not claiming any expertise on FISA or FAA or any of the secret court rulings determining its scope, just trying to figure out ways which collected information could be used to one's detriment. Plus, of course, FISA 2 is always possible, modifying FISA.)