how would 1 tank 3 healers be unfair to them ? do you figure that their queue will increase to 10 -15 minutes and make that unfair - i am not sure increasing the amount of dps in a fight would actually increase the queue time for tanks and healers anyway - i would think it would just reduce the time dps spends in queue
DPS already have many times of spots in LFR then healers and tanks do. Now it would be 21x the tanks spots, and 7x the healers spots. Thats insane.
I can't speak for tanks, but I have heard that they do have a queue time. Your idea is giving tanks and healers more of a queue time, for dps less. I'm unsure what would happen if the tanks and healers required was suddenly cut in half, that is one reason.
Another reason is, having only 3 healers taking care of 25-30 people can easily put much more pressure on the healers. 1 bad healer or a bad healer comp easily has much more of a effect. I can see 2 routes blizzard can take, nerfing it to the point that it becomes really boring for healers, or having it that healers have to be above average of tanks and DPS.
This is why if blizzard goes the route of reducing healers, I rather them do it slowly then just suddenly cut it in half.