I find it interesting people keep bringing up the excuse "You think queues are long now, if they do this they will get longer" which is a false statement. How does it affect anyone that is queueing for a dungeon that you back out of looking for the in progress 2/3 only? It actually gives them the chance to know that the tank/healer that popped in is actually looking rather than skipping around looking for an easy meal ticket.

This in essence doesn't affect the queue at all because you aren't joining full runs to begin with making your statement false and just a bait and switch to try and keep the system from changing.