Back in the day, we reluctantly abandoned PowerPC, UltraSPARC, PA-RISC, Alpha AXP, MIPS... because the bright future was Intel Itanium. Bye, bye, SUN, Silicon Graphics, Acorn, DEC/Compaq, Hewlett Packard, Sony NEWS.
That future never materialized.
That future never materialized.
Arguably x86-64 would have wiped those out anyway, with or without Itanium.
I'd argue what really killed Itanium was the end of dennard scaling. The whole arch was based on clocking faster and faster rather than being a slower, but smarter core. The end of dennard scaling put a ~5GHz cap on CPU speeds, is it's whole value prop didn't make sense against smarter cores that clocked just as high.
IMO, on the technical merits, a lot of those dead archs are just as valid ISAs for slower, smarter cores as x64 is and would have been able to compete. PowerPC and AArch64 are pretty damn comparable.
Without Itanium, those other architectures could easily have had an extra decade or more, and things might have turned out quite differently.