Very cool! This is very very similar to the feedback and annotation feature I'm working on for our product. There's a clear need for this capability to comment (and draw) directly on the design. It just makes it so much easier to talk about something when you literally talk around it.

My inspiration for the feature was that feeling I always got that I needed to walk over to someone's desk and show them what I'm working on on my Macbook or paper and talk through it. Sometimes you can't do that if the team is remote or a client needs to check something out, so you need an approximation of that experience. Making a product around the feature is a great idea.