So you would rather blizzard never do anything else with the blizzard IP in the mmo space? Do you think in 2035 wow is supposed to continue with its 2004 engine? Theres so much more that could be accomplished with an updated framework but propping up a zombie game hinders the mmorpg space as a whole.
Take a look at Unreal 5. Its framework allows multiple instances of content to be simultaneously added and tested. Imagine a new content faster than every 9 months.