The X900 from Panasonic
http://shop.panasonic.com/shop/model/HC-X900K which is from 2012 has it. I've used it before, and the IS is ridiculous. Filters out anything, even a Parkinson patient would be able to take smooth videos
It is a bit strong though, looks a bit artificial cause of the way it transitions from stationary to movement.
If the XL1 has optical IS there is no blurrying. I have uploaded a sample video from the K-3 which shows all the problems of electronic SR, but I'm not at home right now. But if you find one of my videos I've posted here you should be able to find it on my account (kadajawi on YouTube).
Depends on the rig. Some will still let some bumps through that you might want to have filtered out. Say you have rollers and push the camera over the road. There may be some vibration etc., and mechanical/optical SR would filter it out.
Oh and yes, those were camcorders for consumers, so they only had fixed lenses.
The latest Panasonic GX7 I believe has a sensor based SR, but not during video it seems. At the moment only Olympus seems to be doing it. But they have a 5 axis systems which is superior to what Pentax has.
Btw., the iPhone 4s can record at 48 Mbps... It also seems to support a vast variety of frame rates...