Follow comment threads on a post

[cellio]

You can follow a comment thread and get notified of new comments in that thread. I have sometimes wanted to be notified of new comment threads on a post, particularly to monitor things on meta. We can't currently do that. Can we add a way for users to request notification if a new thread is created on a post? The user can then review and decide whether to follow the thread.

We'd need a corresponding "unfollow".

I don't think we need a broader "follow post" mechanism; any changes to the post itself will bump it. I'm not averse to a broader "follow post" if that makes more sense to others or if that's easier to implement.