How long before Mac OS is Apple Silicon only?

[FreakinEurekan]

I think what will happen is that Apple will remove the ability to built Intel targets in future versions of Xcode, but Rosetta will stay around for a while for compatibility with oder software.

Agreed, Rosetta will be around "for a while" to ensure compatibility with Intel code.

Comparing to PPC Rosetta... right now we're in between "Leopard" and "Snow Leopard" - Leopard ran on either either PPC or Intel, and both had Rosetta to allow PPC code to run on Intel. That era ran for about 6 years; back then OS releases were a lot less frequent.

I'd guess the last OS option to support Intel will be somewhere around macOS 15 or 16, so a year or two. Then continued Rosetta2 support probably until... ¯\_(ツ)_/¯ 18 or 19 before that's dropped?

Of course the PPC>Intel changeover was a little quicker than Intel>AS so it's not exactly a parallel experience.