Good speculative topic. I haven't even seen the film camera yet, but it's hard not to think about a digital version.
A FF sensor would be ideal for a number of reasons, not the least for the improved image quality. Theoretically a FF RF could use existing lenses as is -- though there is some doubt how well lenses designed for film work on a FF digital sensor. I see many allusions to this issue on the Canon forums at dpreview.com.
Is Sony working on a FF sensor? Right now it appears Canon is the only game in town, and, as far as I know, they don't sell sensors to other companies. Nikon and several other players get their sensors from Sony, so maybe there's work being done on FF.
So far no one has been able to design a small digital camera in which the sensor could be upgraded later. At least with a Hassy, you can replace the digital back when technology improves, but it's a long way from a carry-around RF.
It's hard to lay down the hard cash on a camera that can't be upgraded when you know the industry is in its infancy and that rapid changes will continue. Unless you're a pro and can write it off...
Bessa T, Zero Image 35mm Pinhole, Canon S90, Nikon F100, Lumix G2