An example of this sort of thing can be well-observed emulating the Nintendo 64. The CPU is a plain-standard MIPS III, but emulating the console's graphics chip hasn't always been accurate for a long time. Disney-released games on the Nintendo Wii would toy with the write-back cache to prevent emulators from booting their games.[1]
I can imagine the largest amounts of difficulty are outside the CPU for a polished-enough project.
[1] https://dolphin-emu.org/blog/2017/02/01/dolphin-progress-rep...
I don't mean to say that given Microsoft's development power it's a massive achievement but it's an achievement and should be assessed objectively, not with snarky comments.
?? No with dos-box you can nearly play all of them. It's just one emulator but then you have also NES SNES GB SGB Saturn Wii PS1/2/3 PSP Wine Atari Commodore etc...
- Paid developers to emulate a Pentium III (original xbox) on a PowerPC (360) in the first place
- Subsequently paid developers to do the effective opposite - emulate PowerPC (360) on x86 (one, series)
Also consider it's far easier to emulate an original xbox on a one/series than it was on a 360