nitpick, they did PPC -> x86 (32), the x86_64 bit transition was later (no translation layer though). They actually had 64-bit PPC systems on the G5 when they switched to Intel 32-bit, but Rosetta only does 32-bit PPC -> 32-bit x86; it would have been rare to have released 64-bit PPC only software.
They had 64 bit Carbon translation layer, but spiked it to force Adobe and some other large publishers to go native Intel. There was a furious uproar at the time, but it turned out to be the right decision.
But they've been on x84_64 for a long time. How much of that knowledge is still around? Probably some traces of it have been institutionalized but it isn't the same as if they just grabbed the same team and made them do it again a year after the least transition.
Rosetta 1 and the PPC -> x86 move wasn't anywhere near as smooth, I recall countless problems with that switch. Rosetta 2 is a totally different experience, and so much better in every way.