1. exclusion list
The only problem I see with this is the possible increase in the amount of time it takes to get into a game for people that have large lists. That will impact the community slightly and the player a little more.
2. chat bans (escalating in severity for multiple offenses) for players that can't chat within the rules
The online poker sites strictly enforce their chat rules. They have to since it is (often) played for real money. If chat rules are strictly enforced then then chat-cheaters will learn - if they want to play and chat they will have to learn the rules and obey them. Or they can play and not chat
@BroncoB, I have a vision (desire, wish) like: "Players from any country of our beautiful World come play 4 Player Chess. They enjoy the game, enjoy the chat, enjoy the club. They play with fair players. If they chat, they communicate with polite persons. They joke, they banter, they smile and laugh. They enjoy and wish to come play again tomorrow."
The reality is: Some strange guys do not share this vision. They cheat, harass, troll and abuse in all possible ways. So, we need to extend the rules, review the reports, etc.
The task is: Minimize the harm caused by pests. And, at the same, do not poison humans.
P.S.
Another way to deal with chat may be: The chat in FFA is turned off by default. There is a button "Vote to turn the chat ON" ("Vote to enable the chat"). If 3 (or 4) players click that button, the chat becomes enabled. So, if a majority in a particular game decides to use the chat, the chat will be working. (The question is: Should we still allow anyone to turn the chat OFF?) But if they enable the chat, they are responsible for what they say in that chat. If they use it to suggest moves, for example, chess.com admins will consider it as cheating.