I'm new to the mediawiki world, and I'm currently researching it in order to decide whether or not I want to use it. I think this extensions is very much needed, as I find talk pages extremely confusing in their presentation etc. I'm speaking as someone who works as a UX Designer and Developer, I'm technically inclined, and I actually know conceptually how talk pages work now, but even so it's very out of step with the UI norms the rest of the web have adopted and a more modern update like this seems necessary.
Also as much as this extension is needed, there is still a lot more features it could use. I think allowing for deeper threading is one thing. Or are these discussions meant to be shallow (in the sense of tree hierarchy depth, not content)?
It might be useful to have shallow comments discussion sections (like you would have on stack exchange or disqus) which have limited nested threads, and then have a deeper "forum" like format which allowed for deeper threading and possibly greater multimedia controls. Just a thought.