So what was up with Orson Pink from Listen? Heavily hinted to be a descendant of both Danny and Clara, which the way canon developed turned out to be impossible. I’m not sure it needs an entire episode to provide an explanation, but something would be nice.

I seem to remember that the Word of God answer to that one was that Danny had a sibling or a cousin or suchlike that he didn't know about (as a result of having grown up in a children's home) and that Orson was their descendent.