Wish List:
Square format, but uses current XF lenses
Largest possible sensor size for XF lenses (Organic sensor allows higher angle of incidence so might be possible to get large with the help of microlenses)
Rangefinder (hydrid EV)
Color x-trans and monochrome x-trans versions
'Monochrome X-trans?' Yes, I know what I said. The Monochrome X-trans is where I think Fuji could get really innovative. Instead of a RGB array, they could do forgo the full-frame UV and IR filters and do them in an X-trans pattern: Visible, Infrared and UV. This would allow for hyperspectral imaging, and for the traditionalists (many of whom are drawn to Fuji's classic looks and handling anyway) would allow for B&W and IR photography in a single body.
(Alternately Vis, Vis+UV and Vis+IR instead of Vis, UV and IR, which might allow for more light gathering and better Vis performance... but the general idea is the same.)
(Reposting this as an updated wish list rather than a thought on the rumor.)