Bitcoin address are one of the main part in the working of the forum. If a person could not verify his BTC address by signing a message means he could not recover his account in case its locked or hacked. It is one of the important criteria to recover a account along with the original email so adding it as an filled on the Bitcointalk profile is a pretty good suggestion.

But this was already suggested by OgNasty to theymos, and theymos thinks PGP keys are insecure and it needs a revision.