As a confluence user, I would like to subscribe to changes for a given set of topics (=words).

If you take a look at "Google Alerts" you will understand what is meant here.

I do not want to watch certain spaces or pages (that I have to be aware of). I just want to be alerted if somewhere new content shows up with the topics I'm interested in.

I can imagine, that users can build this functionality with RSS feeds and tools and filters, but this is too complicated for many users. It needs to become a native Confluence feature - easy and intuitive for everybody.

In my eyes this is a key feature many users will appreciate.