It's pretty clear it wasn't pervasive for ARM because they're climbing to ever higher performance, while Intel reached a conceptual peak in 1995 with the Pentium Pro, and in turn has used mostly Pentium superscalar based cores in their lower performance Atom line. It's implied by the dates of vulnerabilities cited by Google Project Zero I think that Intel's Meltdown original sin goes all the way back to the first Pentium Pro.