Yeah, this sounds amazing. It also sounds like it’s being limited, unfortunately, and will require additional license fees from the OEM on top of the Thunderbolt 4 ports. Hopefully, that’s just for the launch and it opens up soon.
Apple has had “target disk mode” for a long time where you boot one computer into a special mode but that’s basically just for transferring files and not anything like as advanced. I know iPads (and I assume Android tablets) can be a second screen over wireless using third party software but it’s not uncompressed video with disk access last I checked.