Hello,
"PS. I won't be buying a Pegasos, not because although it may well do all as advertised, I can see no pressing reason to start out again with a new platform."
FYI AmigaOne + AmigaOS 4 will also be a new platform.
Why? Because AmigaOne is a new hardware compared to Classic Amigas and developpers will have to port/create their software using AmigaOS 4 APIs to have them AmigaOS 4 natives.
Of course there is the AmigaOS 3.x compatibility, but MorphOS has it also

So in both case, Pegasos/MorphOS or AmigaOne/AmigaOS 4, these are new platforms.
Regards