How does the megamerge handle the case where two included branches overlap in changes and a new commit is made that applies to the overlap?
The mega merge wouldn't handle that based on the way the article shows. You COULD have a revset that includes stacked changes, though. That does work and is what I currently do.
This is something you have to generally handle manually since absorb won't squash hunks with ambiguous targets, but I typically stack these branches and accept the dependency. I have had instances where this has backfired a little bit re: ordering but thankfully with JJ and the very patient little man in my computer named Codex it's easy to reorder them and end up with the same diff