I have been wanting something like this for ages (wide angle converter that's behind the lens)

Exactly what I was thinking of - a K-01 with a built in multiplier to keep the field of view the same as a FF camera.

And perhaps an AF option too with the gubbins out of the 1.7X AF adapter so it'll do auto-focussing with any old Pentax manual lens. Nice - but probably not a commercial proposition.