Having multiple characters is not as much of a thing as it is in other MMOs, so I think the payoff would be considerably small in comparison to what seems like a lot of changes that would need to be made to accomodate that suggestion.
For how annoying the RMT situation is, it is still not even remotely as bad as in pretty much any other MMORPG, so yeah. Also, Gilseller accounts get banned for good if you report them, so that pretty much has the same effect as a whole-account blacklisting.
The countless tells you seem to be getting, Niluriel, can't be from the same account anyway, since you can't be logged on with several chracters of the same account at once. So a whole-account blacklisting wouldn't help with your problem.

Not saying I'm totally against the idea (although the way the OP introduced his idea is not exactly helping ), I just don't see the payoff for all the development time it would take to change the affected systems (like interacting with characters that are not even online, or merely something basic like creating a link between alts which have no ingame link to the main character, and so on).