If I understand correctly, steeping is giving the aroma molecules time to bond with each other. Aromas themselves are PG based. So I would think its logical that only mixing the concentrates before adding the bulk of PG/VG would make a difference in overall steeping time. If the aromas are blended well, then adding the base and shaking well would have to result in instavapeable juice?
In any case it would be a timesaver and less of a mess if you premix a larger amount of a recipe, aromas only.
Funny I stumble on this thread today, as I started experimenting with this