After the trash armour sets for 8.3, I wouldn't be surprised if cosmetic armour sets hit the store within the next year or so, but I hope not and especially not through loot boxes. Remember when they said they got rid of tier sets to give us more set variety? Yet now we're getting 1 set for each armour type this patch with minor differences on the elite/mythic version. Really feels like they're putting little effort into making cool new armour that can be earned in game.
Don't forget they recently included a transmog set in the grossly overpriced digital collector's edition for Shadowlands, as well as a transmog set for the updated recruit a friend system. Both of which actually look like quality sets, rather than glorified quest gear we've gotten in 8.3. Feels like they're testing the waters for more monetised cosmetic sets.