Some games already do some wonderful things.
1. You can blacklist the character, or blacklist the entire account.
2. Right click options in the chat window to report RMT. As mentioned, some games will clear them completely from your log, and even send the basic info in with the report. The sender, you, maybe where he is, where you are, the exact message, time, etc.
3. When characters are deleted, they are auto-removed from blacklists.
4. When accounts are perma-banned, those characters and accounts are auto-removed from the blacklist.
5. A way to flag the RMT'ers against local idiots you just don't like hearing from. The way it is now, to clean up your blacklist, who am I removing? An RMT? A casino? Some smuck I don't want to see? I don't know!
Seems no single game puts the entire package together, but some games do pieces better than others. Doesn't seem that hard to put it all together.