The only way the world could continuously change is via procedural generation, but for those games, the base mechanics remain the same. Minecraft comes to mind, where the 'golden path' is to gear up, find certain items, go through a portal and kill the boss. The levels are generated different every time, but the base steps are the same. I'm afraid it'd be the same with a procedurally generated MMO.

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.