Multi seat with nested servers?

[Phillip Susi]

Only one Wayland server can control a given GPU, but if you have two
monitors on one GPU, isn't it possible to run a root server that
displays two nested servers each on their own monitor to get a multi
seat setup?

Has anyone done this?  What would a good server be to use for the root?
Could you have the nested servers directly bind to their keyboard/mouse
or would the root server also have to multiplex those out to the nested
servers?