I have no interest in Ubuntu mate so I won’t become directly involved in producing installers/images for the distro. I’m not even that interested in the raspberry pi. However, it is cheap, low powered and is a capable desktop machine and those combination of things interest me.
I’ve already raised quite a number of bugs to try and improve things in Ubuntu. Most of the preseeding in the xubuntu installer is to overcome out-dated packages, or missing bits like WiFi firmware. Unless you can get WiFi/Bluetooth firmware into the Ubuntu archives, then some sort of ppa is always going to be needed to make things work out of the box.
Currently the way Ubuntu boots the pi in the server images makes no sense at all. I’ve re-used the flash-kernel package, but it is not ideal. You can’t swap a card from the pi2 to a pi3, and the overlays directory is not updated on a kernel update. Debian’s raspi3-firmware package is an even more crazy way of doing it.
The best long term approach is to adopt grub2 like opensuse. This can be done now in generic arm64. All that is missing from grub-installer is a way to tell it that the media is removable. I’ve thought about writing a patch for that, but since practically every bug I’ve submitted has been ignored, it seemed like a waste of time!
Recently I’ve been messing about with v4l2 which I think I have working. There are some patches to enable this in chromium in Linux that I plan to try. This would possibly be a candidate for a snap?