I'd like to "embed" the structure of a topic for an external piece of content. Would it be possible to render IPS templates outside of IPS (or maybe with an iframe) along with the editor and be able to add/edit comments to this content? I guess I'd have to create a content and comment class in the application to be able to do this.

You could of course output our CSS on external pages, however you will almost certainly be modifying the look of those pages. An iframe is an alternative option, but any approach will require some level of customization.

We do have an enterprise-level remote commenting application that allows you to comment on external pages through our software (stored as posts in a topic). You would need to contact sales to learn more about this if you are interested.