Triggered by Handling creeping questions.
When a question morphs into something different, a "Create followup question" link would open a new question and copy the original question's tags (and optionally content).
The new and original questions would be linked, similar to duplicate question links.
This provides normalized ways for trails of questions which are inappropriate in a single question, or for when a question morphs so much that existing answers are no longer relevant. Followup questions could be asked by the original asker, a user (with enough rep?), from a comment, or...
If a non-asker creates the followup the OP would be notified. Not sure about notifying OP respondents.
This would also provide a way for people to track the genesis of a solution, or to track back and forth if they're in a different stage of the same process.
Robert raises an important point–we can already insert links to/from OP/NP. This is occasionally done. The feature request is for a normalization/officialization of that process–to make it easier to connect narratives that should be connected. Other than providing a "de-followup" action I'm not sure how to police this functionality to avoid misuse/abuse yet.