Sony has released more details on its sensors
here Interestingly it shows that the 100mp BSI sensor is capable of 6fps, whereas the 150mp can do 4fps.
Nothing magical here I'd hazard - simply the size difference taking longer to extract data in the 150 vs 100..
Otherwise the sensors seem to have identical tech/ architecture / pixel size.
In theory therefore the GFX 100, when it arrives next summer, will be capable of 6fps, the Phase IQ4 capable of 4. Both only achievable, if at all, in ES mode and 14bit, I'd imagine.