I find it incredible that World of Starcraft is not a thing. (Starcraft Universe?) Blizzard is letting billions of dollars just sit on the table, refusing to even acknowledge the possibility of its existence.
My only theory is that they didn't want to cannibalize the WoW playerbase, but that's how you get stuck in a rut as a corporation.
About 10 years ago when I worked at Jagex, the creators of RuneScape, there was a sci-fi MMO project (basically sci-fi RuneScape) happening. I didn’t work on it, but a lot of people did, for 2-3 years. It was cancelled before release, I think because it just wasn’t fun enough. When you see a sunk cost like that or Titan (which notwithstanding the Overwatch pivot cannot have been cheap), you get a sense of how hard this is to get right.
I kind of wish there was a "direct to VHS" for video games. You hear about all these scrapped failures, but never get to take a peek.
An MMO might not work, but with regards to Blizzard, there is the example of Starcraft Ghost where they got to the point of releasing trailers and sending empty boxes to stores as advertisements for the upcoming release. I'm sure they'd have sold it if there was a way to do so without damaging the brand.
World of Warcraft was a success because it came out at the right time, during an upward trajectory of MMO popularity, and it was polished and approachable compared to the first generation MMOs.
Since then, the MMO market, to my knowledge, has shrunk, as other genres have become popular. There's no indication that a World of Starcraft released today would be anywhere near successful.
Compared to many other moneymaking genres, MMOs are expensive to build and maintain and difficult to get right. The vast majority of them are massive, pricey failures including one of Blizzard's. I can't imagine any decision-makers at any major game studio thinking not-developing an MMO is leaving billions on the table and, to me at least, it seems they're likely right.
My only theory is that they didn't want to cannibalize the WoW playerbase, but that's how you get stuck in a rut as a corporation.