It's true that if Motif and CDE had been opened in 1996 at the formation of the ironically-named Open Group, a lot of the desktop and toolkit wars could have been avoided. In the form they had then - which ossified and therefore is still basically the form they have today - they wouldn't have sufficed for long, but with the momentum and market presence they had then, they would surely have seen rapid improvement as open-source projects.
Even more radically, if Motif and CDE had been open-sourced in 1994, I think the world would be a drastically different place now.
Imagine copies of 4.4BSD-Lite (or Linux 1.1 + GNU userland) with Motif, CDE, and all the old unixy X11 stuff being available for free a year before Win95 and two years before NT4. (NT4 was the first version of Windows a lot of workstation people took seriously.) Lots of major commercial software vendors already had Motif versions that were more polished than their Windows versions all the way until c. 1998.
With free Unices running on commodity hardware with the leading workstation-class desktop and open source development momentum, the huge workstation marketshare shift from Unix to Windows might never have happened.