If Apple really wants, they can integrate a x86 coprocessor.
Wasted power, wasted motherboard space, increased complexity, additional heat, etc. for everything that isn't native applications. Which should be the vast majority of stuff moving forward.
This will never, ever happen. Apple aren't building these machines for yesterday.
Rosetta2 will be fast enough, and the performance difference if one does exist can be made up by
making the ARM chip faster, Rosetta2 more effective and use of natively compiled frameworks.
i.e., the power/space/heat/etc. that is used for some crappy duct-taped on x86 core is far better put to use to make the native Apple Silicon faster so that the translation performance improves.
Never mind the design issues of memory/bus contention between the native and x86 processors (both processors can't use the same memory without locks or some other scheme to prevent one processor overwriting memory and invalidating the other's internal cache as just ONE example of why this is difficult), additional space for motherboard traces, heat problems, etc., etc.
It's very easy to sit back and say "just add another cpu to the machine!" but
in reality the tradeoffs to that are significant, and it would suck. You would not get seamless full speed x86 performance anyway, due to the above issues.
You'd just end up with a large, hot, heavy machine that was worse at running native software and sucked at x86 software anyway due to all the trade-offs to shoe-horn in an x86 chip and associated hardware.
The translation method Apple has decided on (again, for the second/third time around) would actually most likely be a LOT faster, unless you included basically two entire systems (I.e., two sets of RAM, two system buses, etc. - which is a LOT of hardware that will be entirely useless for native software) in one, as invalidating the cache on a modern CPU makes performance drop off a cliff.
Try turning off all of your CPU's L1/L2/L3 caches on a PC if the EFI/BIOS supports it and see for yourself.