They should.
If there isn’t some form of blacklist it hurt would the community feeling, basically EVERY realm on vanilla had some sort of blacklist, be it through addons, manual list passed around top guilds or in the realm forum.
If they don’t allow it there’s gonna be one regardless, having a maintained one where people can report and help gives a lot of server stability and helps with the community, on top that it would also make people not commit such things in the first place, of course, it’s gonna be strict to get there.
I’m planning on possibly make one but only for level 60s and start a thread on the realm forums, if they allow it, great, if they don’t, it’s gonna exist regardless.
As they already said in the item trading blue post: