Excellent suggestion, I really think this should be looked at. For the new forum of course, nothing is going to be done on this one (maybe this thread would be better on the sub-forum about the new forum).
You can already put an address in your profile but you can't really use it to recover an account.
Well, you technically
can, but since that field can be easily changed, I assume no accounts or almost no accounts have been recovered this way.
If a hacker can access the account,what makes you think he can't simply replace the bitcoin address with the new one ? What if the user loses access to his own bitcoin address ? He will lose the account as people would think he is a hacker.
Additionally,theymos would need to implement forum's own address sign/verifying message service if it has to happen at the backend.
Hence why the OP suggested this system, so It can be changed without the original owner signing a message from his address. If you lose access to the address, well... You can't recover the account (this is what currently happens too).