How would you implement a branched question system?

This is a brainstorming thread. Let’s come up with a way to break questions into smaller questions but without losing the original thread. Or alternate ways of doing this. An easy way to go back and forth with the question and its subsets.

You can go ahead and post ways to do that with the current system as well.

Why could we use such a thing? Not all questions are easy questions. A lot could use subset questions (or parent-child), leaving the original question alone until the user/seeker is ready to address it. If the user is ready to address it, they can go ahead. One example such question: http://www.fluther.com/106202/how-would-you-design-a-distributed-decision-making-system/ with the first responder as the casing point. His ‘answer’ is not exactly off-topic, but not on either. This would also make it easy to mod/move responses to relevant threads/questions for the purpose of organization.