Ambiguous or uncertain dates come up quite a bit, and it'd be great to see CA handle those in a more flexible manner for the purposes of assigning dates to entries. At the moment there's only the options for a specific date or for circa-ing the entire date range in an entry, e.g., "circa 1902-1930."
I'd be able to get quite a bit of use out of being able to use the circa elsewhere in the date, e.g., "12 March 1902 - circa 1930" for when the lower bound is known but the upper is only approximate. At the moment this format returns an error, so we have to use notes to explain dates that are only partially ambiguous.
Being able to use 'floruit' to handle entries where both ends are unknown but there's a firm known period inside that range (such as using "fl. January 1916 - April 1932" for "we can't even guess when this ship was launched and when it was retired, but we're dead certain it was doing stuff between January 1916 and April 1932") would be awesome as well.
Basically one of those situations where a few extra vagueness-related options could reduce the amount of vagueness on hand.