It would be even cooler (

) if it could work with mentions (DBTech AUT mod), but sadly, probably it wouldn't ever work. Linking with profiles is, on the other hand a bit easier. You just need userID supplied (like we have username supplied with $username variable), and you could construct link to users' profile fairly easy.
On the other hand, I'd like that mod checks if the user was previously registered and if was, not to create welcome thread. It looks a bit strange when users registered for years receive welcome thread.