Rosetta was not a naive emulator. It was a dynamic, optimizing re-compiler.

There's two reasons to think that an ARM transition would be easier:

1. The endianness is the same. The PPC/Intel transition required processes to share memory while disagreeing on byte order.

2. Apple controls their ARM CPU designs. They can add whatever they like.

right, and

3. rosetta only emulated the actual app binary; eventually it called in to native libs, so performance for the most part held up really well iirc (for apps, not sure about games)