One relatively easy -technically- solution wold be to make a shift adapter
for the back of the camera.
Normaly PC systems go on the lens part, but the best way to shift is to live the camera on the same position and move the film/sensor plane up-down (or right-left) this makes stitching work more simple.
The Hy6 has lenses with a wide image circle that is sitting there doing nothing -- unless you shoot film, remember? the chemical process -- so the shift would take advantage of, say a 35mm that could become a 28mm with a 2 shot simple procedure, or a nice PC 35mm.
If they make a rotating adapter it meas that there is space -maybe- for a sliding adapter.
I wonder if they have something like this for the RB or RZ so I could mount my 645 AFD on one.
But going back to the lack of a 28mm for the Hy6. When you buy a luxury car -I love car analogies-, like a Porsche Cayman, you are not thinking on going 200km/h all the time, but you know that the car can take you there if you want, same with a USV, how many times you need to use 4x4? This systems are the equivalent to porches and Ferraries. The are made for people that not only work with them but they do so at the top of their field, may it be fashion, landscape architectural or commercial. "Formula 1", level. For most (not me) money is not even a factor.
In this context is where I see a problem with the system not having an available
28mm. It means that all the money in the world could not buy or rent such run-of-the-mill lens for this mount.
I concider 24mm a minimum in 35mm digital. So a 35mm on the Hy6 would be an absolute must for this system (24mm eq. with 1.1x crop).
But as stated, they almost need a 28mm just to keep up in this marketing war.