I think this issue falls into a similar category as support for case-insensitive but case-preserving file systems. Python uses regular file system lookups, but then may need to verify whether it got the right one.

I'd like to request that PEP 3131 is followed as it stands: identifier lookup uses NFKC, period. This gives two issues: a) how can users make sure that they name the files correctly? and b) what if the file system implementation mangles file names.

For b), I'd use the same approach as with case-insensitive lookups: verify that the file we read is really the one we want. For a), wrt. "I'm not able to write U+03BC with my keyboard", I say "tough luck - don't use that character in a module name, then". Somebody with a Greek keyboard will have no problems doing that. This is really the same as any other non-ASCII character which you are unable to type: it just means that you can't conveniently enter the respective Python identifier. Just try importing "саша", for example. Get a different keyboard.