MinUI EX OS Subsystem is a pared down fork of Rocknix used as the foundation for MinUI EX on the Powkiddy v10.
You can grab the latest version here.
Two reasons. The first is practical. Installing a Rocknix update over MESS, or vice versa, would break everything. Rocknix has a built-in feature that prevents accidentally updating from a different distro. The name change takes advantage of this existing feature. The second is expectations. While MESS is just Rocknix under the hood, it doesn't support all the things people love about Rocknix so it would be misleading to call it Rocknix. My plan is to treat it like the frozen firmware of the nand-based devices MinUI supports.