Yet depressingly common in MMORPG circles. People tend to vastly underestimate the amount of work needed to get an remotely playable MMO off the ground.
I've entertained the idea, and the first to requirements that come to mind are advertising money and server upkeep money - then one could start worrying about actually making it
Hear me out: a fully fledged desktop environment, like KDE Plasma or Gnome, but it's a 3D world - "windows" are just walls, the file explorer is just a bunch of procedurally generated condos, and you get a Gmod physics gun to move stuff around.