What if the VR play area is instead surrounded by ultrasonic wave emitters? Something to the effect of what Ultra Haptics is doing but in (at least) 180 degrees.

What if the floor is an Omni treadmill like Infinadeck? Could the emitters be turned up enough to “push” the player back into the center of the play area? I assume it would be noisy but a sound proof headset with noise cancellation could muffle the more audible sonic emissions.

Perhaps a harness hung between the emitters like Spielberg’s Ready Player One to “suspend” a player in the middle of the space.

Something a little less crazy than this GE 360 video:

Seems possible, expensive, and extremely awesome. Want to build it?