I did assume arch maintained the packages properly, or at least enough. I figured it would mostly be maintaining the profile, building the images, and some testing. Perhaps I was naive.
I’d forgotten about FreaxMATE, and I have seen SbK’s spins. So far I’ve preferred to stick with the version Manjaro hosted. I must admit I’ve stopped keeping track of changes to MATE, and I didn’t do it much to start with. You’ve certainly given me a few things to think about, and of course to look into.
Having said that, I’ve been happy with what was provided, I’ve never installed anything MATE from the AUR. As you say, it does seem like I’ve not had a few things, but I never missed them.
As for Arch not maintaining the packages, do you think that means MATE on Arch based distros is in jeopardy altogether, or will they maintain them just enough to keep it going?
I doubt I could maintain them all even if someone let me, unless I had some (perhaps a lot of) experienced help. I can handle packaging relatively simple stuff, at least for myself, but I’m not sure I’m good enough to handle it on this level, or if I have enough time and energy for so many packages.
I should be able to maintain the profile and build the images, etc, as long as the necessary packages are there. Just not sure what problems may arise. I could look into adding new stuff in time.
It’s my favourite DE. Simple, traditional, and they’re not obsessed with trying to redesign everything.
I also think that just a minimal would be fine, but I think there are some useful packages in the full iso. We could perhaps merge the most useful.
I only had to remove 5 packages that are no longer in the repos, there may be a few more for the full iso (I’ll have a look hopefully sometime today). I still haven’t tested the iso properly, but it seems to work.
In case it’s useful, here are the packages I removed:
vino
opencl-mesa
xf86-video-openchrome
manjaro-firmware
systemd-fsck-silent
@ everyone who helped maintain the MATE iso over the years
Thank you. 
EDIT:
I also needed to remove these for the full version, haven’t tested the result at all yet.
extra manjaro-documentation-en
extra steam-manjaro
I’ve seen a couple of error messages from mkinitcpio (happens with minimal and full).
==> ERROR: invalid symlink: '/usr/lib/libnss_files.so.2'
==> ERROR: invalid symlink: '/usr/lib/libnss_dns.so.2'
I found this, where @philm says to use manjaro-tools-git, but it’s unclear if it has anything to do with the error messages as they seem to have nothing to do with the actual problem. Anyway I’m using manjaro-tools-iso-git from the repo.
So far I haven’t seen any problems, but I just booted the minimal iso and shutdown again. It probably won’t be today, but I’ll test it a bit more sometime soon.