>> I just noticed that "project-find-file" is ultimately calling
>> "find-file" only. So it should save the file to minibuffer history if
>> savehist-mode is enabled.
>>
>> But this is not happening in my environment right now. Is this a bug
>> (instead of feature request)?
>
> Recently I noticed this problem too.  So project-find-file-in
> needs to specify the same history variable 'file-name-history'
> as used in read-file-name-default.
>
> Then you could add 'file-name-history' to savehist-additional-variables.

BTW, here is another improvement for project-find-file.
If there is no file name under point, it could propose
the current file name for editing in the minibuffer,
to find another file based on the current file
when their names are similar.