After upgrading all upgradeable packages - pulling MATE and cinnamon, and using MATE for the session, nearly everything has worked.
The only thing that's broken is that my keyboard multimedia keys no longer work with rhythmbox (haven't tried another music player yet)
Looking in .xsession-errors:
(rhythmbox:25554): Rhythmbox-WARNING **: Unable to grab media player keys: GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: No such interface `org.gnome.SettingsDaemon.MediaKeys' on object at path /org/gnome/SettingsDaemon/MediaKeys
Anybody else experiencing this or know how to resolve this problem?