regarding issue28307 - It is not always correct to convert a %d %u %i used to render v into f'{int(v)}'.  That'd lose the TypeError when v is not an integer.

If you are looking at making internal private conversions for the purposes of that issue, I think they should be things that'll never conflict with a normal public API token that might be used in the future. (ie: don't reserve 'd' 'i' or 'f' for internal only use - use special values)  i'm being vague on purpose here as i don't know how f-strings are parsed and tokenized.