the reasoning seems pretty obvious to me.
the 1 item a week will still be in place and it is generally catch up/alt gear so promote more tanks/healers to go as an actual tank/healer and speed up new instances popping. Seems like 90% of alliance gear just rots until it gets unlocked anyways so i doubt this would really have too much effect

Don't think they said anything about it being this way in the unlocked loot alliance raids either

I used to queue as healer for the speed and just greed the stuff i wanted and usually got it already so I really don't see this changing much in terms of actually getting pieces