Having one VR universe from which you can join various worlds where a world is pretty much its own game, and you can join friends in that, and it needs to be "alive enough" to feel like actual social interaction. Pretty much a very big MMORPG.
Several games actually have most of that (including Meta Horizon), except that the games inside are very crude, that the transition from one world to another is clunky, and it's obviously completely lacking emotion (which Meta is trying to solve, I don't know whether they will).
There are indeed other stuff in Ready Player One: - walkpads: That's definitely cool, but they already do exist. They are costly, but same in Ready Player One: Only few people have it. But yes movement in VR is a bit of an issue. I sadly don't expect any progress on that matter (give me a trackball under the hand!), until we can connect to our brain (which I think could be possible 5-10 years from now for simple move forward/backward commands?) - stunts: There are a lot of stunts made in game. I don't think there is any reasonable way to implement that realistically. That being said, stuff like EchoVR are already very immersive imo. - haptic gloves: Okay everyone has it in Ready Player One, and even though we have some stuff, it's nowhere near mass-market. So yes I'll agree this is missing compared to Ready Player One.