That's my guess too. Shadowlands 2020, overwatch 2 2021, D4 2022 - the three biggest franchises in active development with a 3 year release pipeline makes investors happy.
Nah, it’ll be shadowlands - D4 - then Overwatch 2. They said at blizzcon that overwatch 2 was “still early in development”, whereas D4 had a demo and tons of content to release. Not to mention anything they have in-house that they weren’t ready to showcase. I also don’t see a big deal of releasing both in the same year being 5-6 months apart.