SLR mode for highend SLT cameras?

I had a thought this morning; what if the Sony high-end camera like an A99 would have a SLR mode where it could flip up the SLT mirror during exposure.

This would give you the best of both worlds. For the bulk of your shooting you could be in SLT mode and the mirror stays put. This would give you all of the advantages of the SLT mirror like auto focusing and preview. But when you need the best quality possible, the camera quickly flips the mirror up like a SLR and exposes the sensor to 100% of the light for the exposure time.......just like a DSLR.

Of course the camera would have to compensate for the exposure difference but that’s an easy one to figure out.