I have heard that it is possible to work around this (bad, IMO) limitation by going to BfA, going through the tour of Boralus, and then going back to Chomie, when choice of expansion will be open without hitting 50. There is a post here somewhere about it.
Ah yes, here: How to level up a new char in one of the expansions - #7 by Lorran-hydraxian-waterlords