By default, check-spelling only checks files that are present in
git ls-files, so, unless you've manually added files to a git repository and then have a pattern that would naturally prevent adding those same files in the future, you should rarely run into a case where this matters.
If you have specific cases where you feel a need for this feature, please feel free to file a ticket describing your use case. It shouldn't be too hard to implement.
None at this time. I'm still thinking it over. But it'll probably just happen one day.