I'd love to hear every possible way a muted player can now harass you.
Because there's a solution to everything.

The game has "fading", if the devs just wanted to, they could implement a way to "erase" players on your blacklist. If they spam mounts and ride donuts around you, you could just delete them visually, like a quest npc when they walk away and fade off.

If someone is stealing your quest mob kills, players should be allowed to create temporary custom leves. Again, the mechanical platform exists. Players create their own "someone stealing my kills/harassing me" leve with a 10-20 min duration, during which nobody else but their party members can attack/tag monsters.

So now he can't talk to you.
His emotes are blocked.
His bard music turned off.
His mount and char model turned invisible if you so please.
He can't even kill monsters around you.
The list is smarter and won't let you in the same dungeon/roulette.

Anything else I missed?
So this is basically everything the devs need to do.