I red that the codec is m-jpeg to push the 4K through the max bandwith of 175mb/s
I did knew it's possible to add codecs at the canon's OS, it's not cpu implemented ?
Maybe they use the"regular" jpeg output of the processor, the one for stills and bypass the poor line-skipping
and H264 encoding ... The result maybe encoded easily as Motion-jpg ?
Basically, if you look at what the firmware seems to offer, it's what you might obtain when using rafale mode
and buffers at speeds and power that bypass Canon safety rules and marketing positioning ...
You add the codec to put the mjpeg datas at 175Mb/s
and you get an interesting project ....
I can not imagine Canon accepting that someone sells firmware updates for their products !
Or perhaps they will let it go because of the great number of dead smoking Eos bodies
people will get back to shops with no hopes of refunds because of an overheat using a non-Canon firmware ...

Look like also that you have to wait 30s between two shots at full lenght !!!! time to transfert datas from the buffers to the media card.
so, wait 30s between two 90s 2k shots, ok I could manage ... but 30s of wait each 6s in 4k !
That won't work on field !