Now I'm sorry I discarded my own ramble in this thread (dunno if the Mac was 'Too Good,' but if you look at their track record in the crunch time, they had sub-Commodore levels of innovation, while cranking out twice as many "AmigaJr" equivalents, before necessarily alienating everyone with the move to PPC)...
But AT&T's backup system would've worked, of course, because someone paid a lot of attention to ensuring things like billing record types were compatible among versions. Good integrity, like good security, comes by design.
(Re: Linux; conceivably you could 'su' to an 'Internet Zone' user for all your browsing, though that creates some other issues if you want to access the X server... The Amiga 'style' has a sort of advantage there, since some sort of hierarchial jailing -- cross assigns with ACLs -- might work.)