Sounds like sony's going for it:
A big rumor regarding Sony’s upcoming unveiling is that they’re going to be showing us the world’s first pellicle mirror system on a DSLR camera. This means instead of a traditional bulky mirror that swings out of the way — as found in current DSLRs — the Sony DSLR will have an ultra-thin and ultra-lightweight semitransparent mirror that allows photos to be shot without the mirror swinging out the way.
Here’s a photograph of the pellicle mirror found on the Canon EOS RT:
One benefit is a higher number of frames per second and a shorter shutter lag — rumored to be 10fps — since the action of swinging the lens is eliminated from the equation. Another benefit is that the camera would be able to use phase detection autofocus while recording, since light can simultaneously be bounced to the autofocus sensors. Finally, no swinging mirror equals no viewfinder blackout when shooting, less vibration, and less noise — benefits also shared by rangefinder cameras.
I didn't put this in the rumors and news section, because I'm not wanting to talk about the sony, I want to see what people here think of the idea? Would you trade 1/3 of a stop for everything else a pellicle mirror gets you? I sure would. Being able to see your subject as you shoot is awesome. Plus, imagine having your sensor be SEALED in a box so you can't get dust on it? Sure you can then get dust on the mirror, but it can't be sharp even stopped down, at least not as sharp...
Since canon's done it in SLRs before, I wonder if they'll do it with DSLRs again?