The whole separate EF and PL mount thing makes NO SENSE at all.
A PL mount has a very long flange length. I believe it's around 52mm, which is considerable longer than Canon EF mount. What this means, is that a PL Lens will easily work with existing Canon cameras. BUT, and this is a big BUT, Canon DSLRs have a mirror which gets in the way of PL mount lenses because the back element protrudes out on PL mount lenses.
A rental company (can't remember the name) removed the mirror on some 5Ds and 7Ds and make an adapter for the PL mount and it worked perfectly. Of course you can only use the LCD, but for video that's the only option anyways.
I'm assuming that if they do make a video camera, it would be really stupid if it had a mirror in it. It should be an EVF with an LCD.
I guess what I am saying is that without the mirror, a PL mount lens can easily be adopted to the current EF mount.
By making a PL mount only camera, Canon will be seriously crippling themselves because it really limits the type of lenses that can be used with it since the flange length is so long. Panasonic and Sony's video cameras are obviously mirrorless EVFs, with very short flange lengths so any lens can be adopted to it.
One of the biggest advantage of mirrorless cameras is that any lens can be adopted to it in theory and work perfectly as long as they have a manual aperture ring.