It would be tanks. Healers get reduced in number but tanks do not. So unless they nerfed it more to have only 1 tank required or for some insane reason decided AI tanks would be a better choice then it would make the queues worse as you require more tanks to cover the amount of DPS wanting a raid. (17 dps vs 5/6)
I completely agree. I don't know why LFR was designed as 25-man. It's hard for 5 random players to communicate, harder still for 10 random players to communicate, and just about impossible for 25 random players to communicate. It's ridiculous to require a minimum of 20% of the raid to vote to VTK someone before even letting anyone else in on it. At least in a 10-man it would only require two players to initiate a kick, and that's much more reasonable. With 10 people it's much easier to see the troll AFKing in the back of the room. In a 25-man, players are always running every which way and you can't make heads or tails of the fight. 25-man is just too chaotic for random groups.
I remember when LFR first came out and my tank friends were all complaining that they were having to wait in queue. The limiting factor used to be healers. The fact that this current tier's content is tuned to lay 75% of the raid's responsibility on the tanks' shoulders combined with the ability to set loot specializations is what has made tanks so scarce. If tank ratio is so much better why are LFR queues so much longer than dungeon queues used to be?