Honestly, if someone steals my phone I do not care much if that person is able to wipe and sell it, it's gone for me anyhow, it would not return just because the bootloader is locked, but would end up in a trashcan or sold in parts. Until thieves start to watch out specially for jollas there's still a long way to go...

The IMEI solution sounds nice, but a but complicated... is it possible that the user just sets a flag "allow free flashing y/n" and that it is disabled by default? I guess for many people here the risk of bricking is higher than the risk of theft.