In my case, Bitbucket will lose someone who was just using it as a dumb git storage backend, and did not engage with the Atlassian products at all. I assume that they won't be particularly bothered to see the likes of me drop off.

This is exactly how I see it too.

If anything this move might be beneficial for Bitbucket because if there's a 0% chance we would use their other paid products, we were just taking up resources.

Bitbucket’s killer feature is integration with JIRA and the rest of the Atlassian stack, so I doubt it’ll have much impact.

I guess that depends on your definition of “killer”, particularly wrt Jira.

Free private repos is exactly why I was using BitBucket. I will have to think it moving will justify the effort.