Sony published a new Sony sensor roadmap. And it contains first info about their new generation 100MP and 150MP medium Format sensors:
1) New 100MP 44x33mm Medium format Back Illuminated sensor would be announced in 2018 (for the kind of cameras like the Fuji GFX and X1D)
2) New 150MP 55x41mm Medium format Back Illuminated sensor would be announced in 2018 (for the kind of cameras like the Phase One 100XF).
3) New 150MP 55x41mm Medium format Back Illuminated monochrome sensor would be announced in 2018
About the new 100MP sensor made for Fuji and Hasselblad Sony writes:
There is no info about their Full Frame roadmap but the PDF file contains a lot of info on their industrials sensors. Some of that tech will find its way on FF sensors too I guess: http://www.sony-semicon.co.jp/products_en/news/detail/170301.pdf
My wel known stalking point to Sony:
I would recommend you using the large 55x41mm to launch a new medium format system camera.