I really don't see what the issue is here. People are already supposed to update their bios regularly, which by far most people also do, old or new, simply because even many old members gain new stuff and want to add it to their bio, however I don't see any particular reason as to why I should force people to do it on set periods. Fact is many old RPers who return from an absence update their bio by default on their own accord.
I doubt the problem you are talking about is so severe as you make it out to be. It's the exact same principle as with old OP CJ: they were once approved so they can keep them unless that person is clearly abusing them. Even if a bio is against the current rules, at the time it was approved it was allowed so they can keep using it unless that person is abusing it or dropped the bio. A while back I approved an update of a bio of an old RPer who came back (who posted the update on his own accord). There was a mixture of two minor abilities that's not allowed anymore, but was at the time it was originally posted. I saw no reason to revoke it though I clearly specified that it's not allowed anymore, but that I will let it slide so that they know it.
It's really nothing new, it happened very frequently that when we updated certain rules, people who already had a bio from before the new rules, but contradict the new ones, can keep it till they drop the bio unless it's really too OP.
The amount of RPers that has very old OP bios and that are currently active, can probably be counted in the single digits. People have been revoked of stuff they gained a long time ago if they abused it, but likewise I don't really see to make a hassle out of it as long as the people who have such stuff behave.