The ignore user button is silly. You have to click on someone's post to read it anyway. Can't you just ignore it by not opening it? If they do start the "ignore user" button, does that mean that any  thread this user starts, or branch in a thread, that every reply under it will disappear too? What if the replies are from people you like. You may want to read them. Or, are the replies going to stay, so now you have a whole bunch of nonsense posts, referring to nothing. And if the replies do stay and you decide to read them, what about the people who quote the op in their reply. Oops, now you have his post anyway, which you were trying to ignore.
As for if they do implement it, and you also ignore all the aliases of an ignored poster, wouldn't that sort of be a way to out aliases? That would kind of defeat the purposes of aliases. Yes, all the anti alias people are going to say "good," but there are many good practical uses for aliases and that is why they were allowed in the first place.
I say just ignore it by not reading it. Simple enough. It has worked all this time. My .02