Not sure how many will drop back from the main squad, Schmidt seems to like to have a fair few players in reserve at the warm up in case of emergencies. It may mean some shuffling of the squads initially to get the fringe guys more game time, while a few experienced reserves end up held in case of emergencies only to drop out of the squad once the A tour is done.
Either way, I think there are a fair few 10s in front of Meredith for the A side - Edmed, Creighton, Debreczeni, McLaughlin-Phillips, Bowen and Max Burey are all likely to get the call up first. Guys like Edmed, Creighton and Burey are of a similar age with a lot more experience, (Debreczeni older with a hell of a lot more) and even Bowen and McLaughlin-Phillips have significantly more minutes of super (and under 20s). The A squad probably only needs 2 of those guys (maybe a 3rd if they're happy to use them as a utility), but might also have emergency 10 coverage from Stewart, Campbell or someone else depending on selections that leaves them happy enough to leave it at 2.