a pretty simple plugin idea would be a regex to validate post titles, deny the post if the title is invalid

I might try it unless someone else beats me to it

I guess to start with it could be a config file with a dictionary of community name: regex

and later it could be made to use the database with an api to set the regexes, could even allow community moderators to set their own regexes (might need a maximum regex length, maximum number of parenthesis/groups in the regex pattern, and disable lookbehind/lookahead, for performance reasons)