What Vrak meant was you can still join a group, in group finder, with the ignored person if you or the ignored person was not the listee.
If that really works on LFR, that means people that ignore way too much people may have significant longer queue in LFR, because otherwise that would just be prejudicial against anyone you ignore, as at the moment you decide to queue for LFR you’ll be “excluding” all of them from the LFR as well.
Right now, you can only ignore up to 50 people. There are hundreds of people that do LFR, right? That seems pretty far fetched.
You can add them to a friend list and see when they’re online (character) and then just queue for LFR to make their queue longer (since the system will avoid putting these ignored people together). The more people you get to ignore that person, the longer they’ll remain in queue.
How does someone know when that person is queueing? What are the chances you’d be put in the same LFR group in the first place? I would imagine there would be more than 1 group running LFR at a time.