Blacklist + Report in one go needs to happen.
I'd also like to see an improvement to blacklisting in general, so that characters that belong to recovered accounts or to banned accounts are flagged, indicating such, so that I know they can be removed. Sitting at 200 B-listed users is rather rubbish.
Custom chat filters would be good too. I can probably come up with a filter that'll block around 75% of the gil spam if they give us a decent tool.
I'd also like the ability to just block tells entirely without going busy. That prevents me from getting party invites apparently, which is a pain. And I could disable them from the chat menu, but I don't just want to hide them; I want them to be able to even send them to me.

And finally, create a system that auto-flags an account for review if it messages more than X number of people in a single day, or if it messages Y number of people with the same message (or 90% similar).