In the future all Windows applications will be sandboxed, MSIX was the first step merging UWP and Win32 worlds after the failed experiments with Project Centipede, Android and Cocoa integration into Windows 8.x.
The upcoming Windows 10X, uses sandboxing for everything, including Win32.
This is intended for languages that require some kind of interpreter to run, and to have OS integration out of the box as if they were "native" apps on Windows.
That doesn't really answer any question i made though. Is it something specifically about Windows 10X and MSIX limitations? How would i use it? Etc (i do not want to repeat my questions, i'd just copy/pasting them :-P).
It's a fix for a limitation of the Windows app model, i.e. to the OS's knowledge of which executables, processes, files, etc. logically belong to which apps. MSIX is how you register an app with the OS so in that sense it's about "MSIX limitations" but apps/runtimes not installed with MSIX still have the same problem.
The OS knowing what's logically the same app vs. separate apps is a prerequisite for 10X and sandboxed apps, but there are other features usable by non-sandboxed apps that depend on it too.
The upcoming Windows 10X, uses sandboxing for everything, including Win32.
https://www.youtube.com/playlist?list=PLWZJrkeLOrbZ3CMHpbglE...
This is intended for languages that require some kind of interpreter to run, and to have OS integration out of the box as if they were "native" apps on Windows.