>> Probably. Would you like to propose one? So that I have something to
>> compare to, and have something specific to put to the vote as well.
>
> Ok, something like this:

Here is a more tested patch.  It supports these cases:

(setq project-switch-use-entire-map t)

C-x p p C-b - should not include current buffer in the list of another project (bug#58784)
C-x p p f M-n - should fetch the right default file name (bug#58784, bug#63829)
C-u C-x p p f emoji TAB - should include ignored emoji-labels.el (bug#63648)
C-x p p C-x d - should visit another project's root (bug#63648)

The same with frames:

C-x 5 p p C-b
C-x 5 p p f M-n
C-u C-x 5 p p f emoji TAB - should not show completions in another frame (bug#65558)
C-x 5 p p C-x d