Sony's SLT is very different from the Canon film pellicle mirror cameras.
Canon had a semi-translucent mirror to direct half the light to a viewfinder, and the other half to the film - the upshot is no mirror slap, so higher frame rates are possible and also a more stable camera, and also no viewfinder blackout. The downsides are a darker viewfinder and less light hitting the film.
Sony use the same type of mirror to redirect half the light to a dedicated AF chip, and the other half to the sensor - there is no OVF. So its basically a mirrorless camera in a big body and only half the light sensitivity it should have. A mirrorless camera with on-chip PDAF is much more sensible if you're going to dispense with the OVF - which is precisely what the A7 and A7r are all about.
This new Canon patent is almost a digital version of the film based Canon pellicle mirrored cameras, but with one major difference - the mirror has variable reflectance/transmission. If it could approach 100% reflection while composing, you've got pretty much a conventional bright viewfinder, and if it could electronically switch almost instantly to almost 100% transmission, pretty much all the light can hit the sensor for the shot.
Much higher frame rates, much shorter shutter lag, and no vibration due to mirror slap could be on the cards.
IIRC Sony claims only a 1/3 stop of light lost by the mirror. Apparently only a enough light to work the PDAF. The bigger issue for some was the ghosting and random artifacts that occur in some lighting situations.