What
After browsing various sites and tutorials, this is the distilled TLDR version of how to get X2go remote viewing of a MATE Fedora 26 desktop
Commands
Some of these might not be strictly required, but based on the history of the VM I just used (I didn't even run the updater):
sudo dnf install openssh
sudo systemctl enable sshd
sudo systemctl start sshd
sudo dnf config-manager --add-repo http://packages.x2go.org/fedora/x2go.repo
sudo dnf install x2gomatebindings
sudo dnf install x2goserver
sudo dnf install x2goserver-xsession
Once done, reboot. Something doesn't work until this is done.