The expansion is most likely going to come with a free character boost, so you'll be able to get a 110 Zandalari Troll or Dark Iron Dwarf on day one. If you mostly care about being able to play the expansion content right away, it doesn't really matter all that much that you won't get the heritage armor from leveling 20 to 120. Ultimately the only part that is inconvenient is purely cosmetic and I feel like most people should be able to live with that.