That seems to be related to a rule that FAA added after some other incident but the MAX was not forced to follow this new rule, it is not an issue that was discovered when scrutinizing the MAX.
What I have read indicated that it was a violation that was missed:
> During the original design and certification of Boeing’s 737 MAX, company engineers didn’t notice that the electrical wiring doesn’t meet federal aviation regulations for safe wire separation. And the Federal Aviation Administration (FAA) failed to detect Boeing’s miss.
Boeing did try making the argument that since their 737-NG planes were produced prior to that rule, and they're safe, that the MAX shouldn't either. But it was part of the regulations when the MAX was designed.
Yes. The FAA's proposal also involves physically re-routing some cables, which is (as far as I can tell) completely non-MCAS-related.