I don't mind how popular the genre is right now, a fun game and a few streamers and popularity jumps from one game to another in a heartbeat.
My only concern would be that when it comes to Blizzard i guess they'll try to deliver a finished AAA product that can end up competing against early access games that are actually cheaper, more accessible, fun and usually developed by very few people that are way more open to feedback and closer to their own players than a big company. But survival games can come in different flavors, so i guess that highly depends on what their goal is, we don't know enough.
Anyway, trying to do something new and different is good for them.