I'd like to be able to filter my key exports based on calculated validity (e.g. only export user IDs that have validity full or greater).

I think the simplest way to do this is to add a keep-uid export-filter property valid, which is a boolean, like primary.

It would obviously be more flexible to have a filter that does some sort of numeric test against calculated validity, but that raises a separate set of complicated UX questions, and the only filter i can really imagine using is "validity full or more" anyway, so i'd like the simple use case to be easy to do.

Seems like this sort of filter would also be useful on import, though it would require calculating the validity as the certificate is processed (not relying on a cache).