I've been saying this here and there, but I'm much more interested & looking forward to a MetaBones SpeedBooster for V-mount lenses.
With the same ~0.7x reducing factor of the current ones (FF -> APS-C) but built larger for V lenses, we can have an "effective" full-frame square MF camera with a "crop" square MFDB, like CFV, privded somebody designs a nice "body" to be placed between everything.
The setup would look something like this:
Since the SpeedBooster requires a much shorter deistance between its rear element and the plane of focus, extant V bodies won't work, meaning somebody would have to design & make it. I still think it's more likely that that would happen than somebody give us a 56x56mm sensor :p