A900 Replacement - Option to flip up SLT Mirror?

If the A900 replacement cannot have a hybrid EVF / OVF, then my next question is:

Can the A900 replacement have an option to flip up the SLT mirror and still be able to work and auto-focus?

As an A900 owner, I'm simply not in favor of losing any amount of light to the sensor, unless the camera could increase its dynamic range a couple of stops...