IIRC host migration can already be done, I remember seeing a template for it somewhere.
But host migration is a clunky and lossy process, regardless the platform you are developing on. This is why commercial games pretty much all use dedicated hosts instead, which you can
(and should) already do with the existing plugin as is, rather than try to build and rely on a host migration system.
The multiplayer plugin is probably the lowest priority to be updated so I wouldn't hold my breath waiting for it. It actually has quite a lot more functionality than people give it credit for, high expectations aside. The understanding of core multiplayer networking principles is the hard part .