I can guarantee you that popular DNS resolvers (think 500b+ transactions a day) do have this feature!
Don't want to say much more due to it being my job, and I don't want to give away too much.
Don't want to say much more due to it being my job, and I don't want to give away too much.
It provided value by answering my question concerning serious downsides to providing optional post-TTL last-known-good caching within a DNS resolver. The answer is implicit in that a major DNS resolver provides exactly this functionality.
A little more information, considering it is public. (I had to double check if it was)