Something like this would definitely make me move towards using Disqus.
Two other (smaller) problems I see:
Disqus doesn't use my registration system. Currently I have bbPress and Wordpress using the same registration system.
This makes it convenient for users to contribute to comments and the forum--because they automatically have an account at both places.
Using Disqus would change this. I don't see an easy solution here--and this isn't a problem for most people.
One possible thought is expanding the API, it seems pretty limited right now: http://disqus.com/developers/
I think it would be best to provide a standard solution that works for most users. The other chunk (people like you/me) can develop on top of the API creating whatever custom solution we need.
This is a win/win.
The other problem I see is being able to customize the comments.
I haven't played with Disqus enough to know this--but being able to customize the comments (IE: Strip out CSS and customize with my own, re-organize using my own markup, strip JS if I choose to) may be an issue for me.
Disqus looks the same across every blog I visit. Adding a way to customize comments would be extremely helpful.
As joshwa said, both of these problems could be solved with a better integrated WordPress plugin. Not to mention it could easily be extended with a more developed API.
The good news is Disqus seems to be listening. I see them replying everywhere they're talking about--which is great.
These are the primary reasons holding me back from using Disqus, any thoughts on adding these Disqus?