You can just right click > report RMT now
Yeah I do that. My whole point I guess is I don't want to have to constantly do that or blacklist then clear the blacklist. People shouldn't have to deal with it. Chat filter would put gil spammers out of sight out of mind for everyone. I'm sure it would be easy for them to implement it.

For now though I just followed HyoMinPark's advice and made a city log that doesn't have /say /shout etc... Issue with that though is I would miss all the /say and emotes from friends while in the city.