Your suggestion actually goes deeper than just QA. I was thinking the other day that one of the problems of Steemit is the fact that it only presents one view of the content, a stream of general stuff.

What makes Reddit and other networks really interesting is the fact that you can subscribe to your fave categories, and so follow only stuff you are interested in. So rather than using just a tag, why not implement a full blown sub system, where folks can subscribe to their custom feeds of topics they like?

Or am I missing something?