@Danne Have tested your 4k build and it works, see video. Able to record 4 or 5 frames at a time at 4096x2552 resolution at 9fps. That's the first time I've ever recorded anything in 4k! Liveview is scrambled, but with global draw on it works - you get the usual pixelated low fps preview.
In one of the exterior shots close to the horizon area the focus pixels make an appearance (small area only). I've looked at the various options to remove these in MLV App but they don't seem to go away.
Also, I tried to see if it was possible to select a lower resolution with this build (2.5k or 3k), but it didn't seem to work so I did no further testing. I'm assuming this 4k build is only designed to work with 4k resolution?
Understanding how these registers works because these registers controls write & read speeds .
Or someone helping me with this. 
Thanks for bringing this up @Bilal. I guess that's probably the most important next step to take in order to make higher resolution recording feasible. What sort of coding or steps would be needed to help you with this? I don't know how to help but maybe could ask around, although I imagine anyone who looks at this would need to have specific knowledge about coding for Magic Lantern?