Of course it doesn't, I'm not denying that. Popularity doesn't effect the fact that the game has no meaningful history with Nintendo at all. The most it should get is a costume, like Sans. It doesn't deserve a full character slot.
My dream is after the Smash series of amiibo are done, Overwatch is the next big amiibo series to keep up sales. With over 30 characters it could really revitalize amiibo, which hasn't much success outside Smash. Maybe they could unlock special loot boxes or skins. Blizzard has already made the Loot Goblin amiibo, so it could happen.
Blizzard is done with HOTS. Blizzard doesn't want to show off the game they refuse to invest in at this point. So many issues they could fix in HOTS but wont because it's just being maintained now, with fully-funded development.