Mike Tapa at MTF Services just mentioned they should be ready in a couple of weeks. Great news to 5D shooters dying to use their favourite L-series lenses.

I wonder if I'll be able to use my Zeiss Contax lenses with a C/Y to Canon adaptor on the MTF?

I think in the past MTF EF adapters have not been able to adjust iris.

need to wait for Birger for that.

Right. The aperture has to be pre-set. Mike suggested using a Canon body and set the desired aperture on the lens, then hold down the preview button and remove the lens. The lens is now set at that aperture.
Not ideal unless you're working on stage where you can light to the same stop for every shot. On exteriors, I imagine a variable polarizer/ND is the only way to adjust exposure, unless one wants to keep changing shutter speeds or reboot the aperture by putting the lens back into a Canon body.

Zeiss lenses with Canon mounts will not have this problem.