GMail feature request

When replying to a message in GMail, if you change the subject, GMail creates a whole new thread, fully independent from the original thread. In fact, after you've done it, you can't tell that the message has been replied to at all.

Feature request: when you change the subject, automatically create a link to the new thread, right below the message from which the new thread was spun off.
Plus (optional): also create a backlink, at the top of the new thread.