I have no strong opinion. I found the discrepancy when reviewed one of Mark's PRs. I was surprised because I did not know that "N" is supported.

On other hand, there are reasons for supporting upper-case variant of "n" if we support upper-case variants of "e", "g" and "x" (formats which produce output containing letters).

There is an alternative solution of the problem solved by upper-case variations of formats: add a special converter for converting a string to upper case, so for example f'{x:12.8E}' could be written as f'{x:12.8e!u}'.

I prefer -1 or 2. If we choose deprecation I prefer adding an upper-case converter.