You don't seem very far along with this (one commit to the flavour-maker code, and no changes to the ppa) so can I make a request? Ubuntu-mate has undoubtedly been very popular on the pi, but its hybrid nature is very confusing and actually works against getting better support in Ubuntu. There is no reason to use the same kernel as raspbian when Ubuntu builds its own kernel especially for the pi. This works well in armhf and arm64 as I have demonstrated in the xubuntu installers/images I built for 18.04 (AArch64 on Raspberry Pi 2 (rev 1.2), 3B, 3B+ ). These were quick to build because I used the standard Ubuntu build packages/scripts. Why isn't an official armhf/arm64 ISO produced at the same time as the other architectures? It is certainly do-able, it just needs a motivated person (preferably inside canonical) to bang heads together and make it happen. Please start building Ubuntu-mate like the official server images (using the Linux-raspi2 package).