It's not very interesting before it's 3.8 compatible, that's true. But when it is, having a port makes a very big difference:
Anyone wishing to target MOS, AROS and AmigaOS at the same time will need their software to work with Zune to have it work on AROS.
No, when Zune reaches MUI3.8 level, anyone wishing to target MorphOS, 68k Amiga OS, AROS and OS4 should have their software work with
MUI3.8!
If by then any MUI3.8 applications doesn't compile for/run on Zune, then Zune is broken or lacking stuff, as simple as that. It's the
MUI API that needs to be intact, regardless the underlying software (be it Zune or anything else).
This confusion of API's and underlying software sounds very familiar to the "oh, but MorphOS is not Amiga because it doesn't have the Amiga sources" nonsense, completely disregarding the fact that the very same Amiga API is completely re-implemented by using *other* sources, and it works just fine!
Not only would it be impossible (or have to be done in a very weird way, as already explained by others) to run Zune in parallel with MUI4 on MorphOS, or "MUI3.9 + some 3rd party MUI4 additions" on OS4 for that matter, it would also be *totally redundant*, since all MorphOS developers, and OS4 developers too, can *already* target their software for the
MUI3.8 API if they really want to. No need to squeeze in some Zune SW with a hammer and a shoehorn, that provides a fraction of the functionality compared to what's natively available, and in a worse way. Crazy!
If Zune is available on all three platforms, then they get a choice: They can target Zune on all of them, as the lowest common denominator, without worrying about incompatibilities, or they can target three different libraries with varying capabilities.
In that case, it will be
MUI3.8 that will be the common denominator. Zune is merely a re-implementation of MUI. In practice, this will mean MUI on MorphOS and Zune on AROS, both using the same API (if Zune is done right). Why is this so difficult to understand?