Apple obviously had an advantage as they also control the hardware (and Arm helped by adding some extensions to simplify translation); significantly easing two difficult parts of translating from x86: TSO and status flags. AVX is somewhat annoying (256-bit regs -> 128-bit regs, frequent merging of scalar values), but manageable.
> You would like to be able to precisely handle exceptions (especially ones caused by invalid memory accesses) while presenting a userspace exception handler with an architecturally valid state for the source program.
This is absolutely annoying and makes many optimizations much more difficult as a lot of additional state needs to be kept around, either for real or in metadata for reconstruction (including weird status flags, fun with partially written flags (inc/dec), maybe-written flags (shift/rotate), etc.). Does Rosetta 2 always have precise status flags (including PF/AF) at every possibly-faulting memory access? (This should be rarely needed in practice, so I've never implemented flag recovery in my own binary translators (primarily for research, Instrew but also non-public).)