I feel like a combo of large scale procedural generation mixed with a large library of hand crafted content is needed. I was just thinking about this today. I'd love an MMO so large that I rarely meet other players unless I want to and with quests that are random, unique, yet meaningful.
If it's hand generated, realistically they could only do a new map once every period, and the first guides would be online within hours of release. I believe Fortnite does or used to do this, making big map changes every season.