Thank you guys for your advices.
Regarding the focus screens - I plan to get a 5d3 in the future (hopefully), so changing the focus screens is not a reliable option when investing in an expensive Zeiss lens, and I still feel like i need to stress my eye, especially in a dark enviroment when focusing via viewfinder. The Zakuto EVF is too bulky (we're talking about this: http://www.zacuto.com/wp-content/uploads/2010/09/dslrevf.jpg , right?). The external focus screens are not an option either (at least for me).
I'm not a videographer, so I would use it only for shooting stills and I'm totally attached to looking into a "hole" in the camera (the viewfinder), or tripod + live-view.
So, it looks like there's nothing on the market that would fit my need?
Which Zeiss were you planning to get? I have gone down the Zeiss route with my Canon bodies before; in the end, I did not feel Zeiss did anything better than the top Canon lenses. In fact, I felt top Canon lenses had more neutral color rendition than Zeiss. Throw in Canon AF ability and how expensive Zeiss lenses are anyway, and there really is no reason to go with Zeiss IMO.
With Zeiss manual focus lens and adapted Canon manual focus lens, live view focusing with zoom-in is the way to go for critical work, and one does not necessarily need tripod for this..