I think it looks pretty good, along the lines of commenting in sound cloud.
I am not sure how you will get on selling it as a service though. Having to jump out to another service to do this is not desirable, nor is losing control of our content / locking it into another service.
We use Kaltura and I am sure something like this could be done with a Kaltura plugin for Moodle. I had wondered if Kaltura is what you are using on the backend?
i think at some point YouTube / Vimeo will catch onto what soundcloud have done, if they do you would lose your USP.
So yes, really like the concept. I think this is the way commenting on videos will go. However, in such a competitive space I think you will struggle to build a hosted service around it.
An alternative could be to drop the hosting and work on something that integrated with multiple platforms (if API's support that) so you could discus Kaltura, Youtube, Vimeo in one place perhaps allowing comments via Twitter etc. no idea if that is viable, just a wild idea