I think Legion is a step in the OP's direction, but they are testing the waters a bit. As mentioned, zone scaling and artifact weapon basically mean that player power doesn't really change with xp increase. And then we have Suramar, which is a huge max level exploration zone which introduces some important story. You could imagine removing the xp bar entirely and have all zones feel like Suramar, which develop story through a lengthy, story-focused questing arc. Along the way, you earn reputation with factions that have great items for increasing player power. Seems like a direction WoW could definitely go.
Of course, you wouldn't want heroic/mythic dungeons and raids to be available immediately after expansion release. The top players would just skip the story entirely and jump right into gear progression. And because the top players do it, the whole try-hard community (I say that without meaning anything derogatory) will also do it. And suddenly, WoW is even LESS about story. So I think you'd want to have story unlocks to heroic/mythic dungeons. (And I personally like the idea of having a solo-scenario at the end of each zone where you recap what you accomplished, have a minor climax, and then motivate killing dungeon bosses in that zone.)
But yeah, this is a direction WoW could go. Seems like it could be okay.