One thing I wish Canon would do is maintain a consistent approach to their button timers. The allocated button, such as ISO, gives you a timer when it's pressed and released but if you change the ISO to the set button it doesn't unless it's a 1 series. Surely I'd would be common sense that, if you offer the ability to customise the buttons, to maintain the timer on them.
It's fine when I use my 1DXs together but when I have a 1DX and the 5D4 on the go I'm always forgetting that I've got to hold the button down. How hard can it be, it's not rocket science.