Profanity isn't bannable, that's already been set.
There's been some developments in the time since the post - Mojang has (somewhat) clarified that their intent is more for severe offenses (actual harassment, real threats, etc). Of course - what they say and what they do are two separate things.
However the good news is that it does look as though there will be an opt-out, as only "signed" messages can be reported. Basically if a message is signed it has a digital signature with it that confirms that "yes, this message 100% came from this user". Unsigned messages cannot be reported since there's no way to verify. And as of right now, PaperMC 1.19 builds allow for message signing to be disabled (and in fact it's setup like this by default), which effectively means all messages within that server are not reportable.
As long as this doesn't magically change between now and release, it won't matter a great deal what they consider enforceable - as it won't have any effect in CU (and likely many other servers too if I had to guess).
So I suppose the tl;dr is that as of now, it's looking like it won't be a very big deal at all ultimately - servers that don't want to use it likely won't have to, and the pg-13 servers that do can have fun with it I guess