I was wondering if it would be possible to use the existing zoom box function but magnify the area inside the box rather than having to zoom in and out which can take time. I think that would give enough info at 5 or 10x zoom to be able to focus while being able to check composition at the same time, also the box could be moved around with touch screen and it could be toggled on/off with a function key. Would this be possible?
The idea is not bad, but I think the live view magnification is implemented like it is for a reason.
First, when the camera is in (normal) live view, the sensor is read out in a way that reduces power consumption somewhat. That means, line/column skipping and/or pixel binning is used to reduce the amount of data that the sensor outputs and the DIGIC CPU processes. When you enter magnified live view, only a part of the sensor is read out - the "window" that is visible on screen.
The older DIGICs (such as the DIGIC 7 of the M6) are likely not capable of processing 24+ Mpixels worth of data while maintaining a sensible frame rate (25...30 fps). Same goes for the sensors in those cameras.
If you don't have full sensor readout, you won't get sharp details when trying to magnify part of the live view image.
Then, there's the other obstacle: you'd need to program the sensor readout, pixel processing yourself as the firmware routines probably don't provide all the functionality you'd need. Even if there's some knowledge about those details (researched and implemented in Magic Lantern), that research has not been done yet on DIGIC 6 and later processors.
