OK, I guess I'll be the one to start things going on the COFF list.
What other features, ideas etc. were available in other operating
systems which Unix should have picked up but didn't?
I've been thinking about this many times in the past and I've found ever the same problem: the framework of reference.
My choice has always been to use the timeline as the first variable; and second, the characteristics, power and size of the hardware on which UNIX would run.
But I think that a third variable is needed: other hardware systems with other operating systems running.
And as a final step, a detailed list of the aspects and features os these OS's and UNIX selecting the common features of all... or the uncommon.