Sometimes, answers to the OP question can lead to
- new questions, related or totally unrelated to the original question,
- open discussions, just loosely related/unrelated to the original question.
I'd like to propose some options like
- "branch into related question" (links back to original question)
- "branch into unrelated question" (links back to original question)
- "branch into discussion" (the original question is not so important anymore and the aim of this branched off discussion is not to answer the original question anymore)
By "discussion", I imagine more of the classic web discussion forum, where every reply gets appended at the end of the discussion list (so, up/down voting does not change the display order).