70s will most likely die and won't make it past mop.
Even if they don't screw everything over, if they do what they did last expac and give the earliest expac to all users for free then all the battlechest capped players, who bad as they may be, fill up the random BGs and reduce queue times, will disappear.
The remainder of the twinks will all roll the best specs and the bracket will become stale and die really fast. I watched 60s die out incredibly fast when there were 30+ paladins on the alliance side of AV... when 60 paladins could do 9k avenger shield crits. They camped graveyard in wsg, we stopped queuing. They merged all battlegroups together, queues resumed for under a month before we (Horde) stopped queuing as they graveyard camped.
In the 70 bracket there are people who DDoS and graveyard camp and the community is worse than that at 60. Noway will it survive if wrath is given to all newcomers.