>> do we know for certain the level of compatibility between MUI4 on AOS4
>> and MUI4 on MOS?

> That [...] really only concerns the users of OS4.

...which eliyahu belongs to, which in turn might explain why he is concerned ;-)

> Plus, they don't need the source to re-create how it works.

You *can* reach 100% compatibility in a reimplementation, yes, but that doesn't mean it has actually been achieved with the OS4 version of MUI4. The question about the compatibility level is a valid one, I think.