> desktop ARM is likely to have the same problems as desktop PPC, namely
> that those using them are big companies who can design their own support
> chips and quickly work around any hardware bugs. And will promptly close
> off their own designs so MorphOS would take years to run on them anyway.

I'm not sure that "desktop ARM", in contrast to old "desktop PPC" (aka G3/G4/G5), will necessarily have "their own support chips" given the trend towards more and more integration. As a result, "desktop ARM" could simply lack those means to lock out any not their own OS as the I/O controllers etc. are part of the "desktop ARM" SoC documented by its vendor for 3rd parties.
Also, I'm not sure that, in case of "desktop PPC", "their own support chips" were a real obstacle for porting any not their own OS to it ;-)