How does this differ from the project it forked from (MenuetOS)?
Menuetos abandoned its 32bit version (the one that was open) to focus on 64bit, which is not, and even has a clause in the license that prohibits disassembly.
I'd say RPI it's the best in that regard. Also fully fledged Linux there, not some pet project OS.
I'm not sure if it's actually more expensive to find VIA et al based systems for cheaper than NUCs?
But there's Vortex86.
Not much educational use to get from a system that is closed source and has a clause forbidding disassembly in the license.
Regardless of being closed source, I'm going to guess that it would still be highly educational to learn Assembly programming on a system that makes it a first class citizen where you just boot into the OS that already is entirely built around ASM. For really simple stuff, a simple microcontroller might be better, but I'm sure some folks are more interested in building desktop apps.
Educational use most often means you learn how to use a software, not how it's made.
Autodesk gives free educational licenses for its software and I saw no one saying it's of no use.