Fallout 76 have a interesting take at hybridicing multiplayer and singleplayer.
Like. You know in multiplayer games you can’t do a event where a whole city is under attack by a dragon. But in a instance with only 20 players, these things are possible. Or nuke a whole city.
The world is filled with monsters of your level. So if a level 20 and a level 40 walk in a new area, they will fight monsters level 40. It will be fun for both players (but challenging for the level 20, of course).
I am level 42, poopshocked this game hard. And I saw moments where this particular design broke the wall that mmos usually have and restrict what mmos can do.