I was actually thinking about a feature like this the other day
Would be really nice to be able to sort friends by "date added".
I guess sorting by logged in/last seen, would be really useful aswell if you need to get in touch with a friend for some in game help or whatever, asap.
Sorting by their join date is not something I would care for, but if people would use that, then why not.
Voted yes ofcourse.