Is there really a lot of crossover from casual Hearthstone players to casual HOTS players, though? At least Blizzard's other games are somewhat similar in certain ways. HS is completely different than everything else. Not saying it won't happen, just not sure if it'd be as successful as something like the OW event considering how similar the two games are.
I really hope they prioritize Overwatch heroes over the next year. There's some good ones there. I also have never played Starcraft, so I care not about those heroes, and there's only a couple I'd like to see from Diablo still. That leaves OW and Warcraft, and I'm all about the OW heroes.