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