The next release of MESSUI is expected to be 0.220 on or about the 25th of March. It will no longer contain all of MESS; it will be filtered to only contain systems that have been tested to work. The filtering will be done by source code, so even if only one system in that source works, all systems will be included.
Further filtering - the system must start up, with working screen and inputs. If the system requires a disk to boot with, a suitable disk must be included in the software list.