I've brought this topic up a couple of times, but have never had any feedback. Players with multiple accounts with the same billing information should be able to make at least one character transfer. Obviously there are concerns with RMT, but that is easily combated with the following conditions.
1. Same billing information on both accounts.
2. Both accounts must have had the same billing information for at least 3 months prior to the request.
3. There will be a fee ($50) for the move
4. There could be only one transfer (with either account) once per 3 months
If that's not possible, at least allow players to log on multiple characters on the same account.