The difficult part is simply understanding what Canon code does (and what we have to change to fix the preview).
Those numbers from the logs and adtg_gui are like Chinese to all of us; the trick is to fiddle with them until a tiny part of them starts to make some sort of sense. That's how we figured out how to reconfigure the sensor to 4K in the first place
Some useful tricks: comparing all those numbers in different video modes (adtg_gui has a simple register diff tool), recognizing values that could look like resolutions, logging the I/O activity in QEMU, or analyzing the still photo mode first (it's simpler).
And, of course, don't give up after reading a single post. Make yourself comfortable with what's happening in the Reverse Engineering area. Some relevant threads are linked in the first post; make sure you can follow them.
Of course, you will need some basic programming knowledge.
Bottom line: the real-time preview is not implemented because... I have little or no idea about how Canon configures the image processing path.
