Hi Alex,
I feel your pain! Having the NA-GH5 (M18) and the NA-Flame housing for my Atomos Inferno - also M18. Having gone through the expensive of getting them upgraded to M24, I was very intrigued why also.
a) Physically a HDMI 90' Plug won't fit in a M18 hole - tried it, even a normal flat plug won't fit
b) HDMI Mini and Micro plugs aren't all that compatible with signals past 14Gbps - so they don't support 4K or 4KDCI @ 60p at 10bit.
It's not just Nauticam's issue, I tried trouble shooting the issue with so many different cables, adaptors etc to see where the issue lay, only thing that work was full sized plug based cables - I didn't find one micro to full sized hdmi cable (even if marked as Premium HDMI) that would work, even using a simple micro > full adaptor.
So the only why for Nauticam to provide us with support for these new 4K and higher signals was to completely move to a straight-through, full sized 'Premium HDMI' cable - even adding breaks in the cable can degrade the performance rendering a cable not compatible with 18Gbps.
More info - https://www.hdmi.org/spec/premiumcable