Let me explain our use case in more detail.
We want to provide a “discussions plugin” like Disqus or Facebook do, but on a small scale targeting sites that share our principles. Users brought to our Discourse by one site would then get to know the other sites, and the idea is to create a critical mass of active participants in times where most of these blogs must rely on Facebook, Twitter etc to get feedback.
In Redirecting... you can see what we have got currently, a combination of blogs, each one run by different 3rd parties, some connecting with JavaScript embedding and some with WP-Discourse. We are working to bring more blogs.
Each blog has its own category and its own user to create topics. With the WP-Plugin this can be achieved. However, with JS embedding it is possible to define only one user for all of the allowed hosts, not one user per host. This means that we need to user a generic user and then change owner of the topics created manually.
Our assumption is, since we need to touch the database, the UI and something more to allow one user per host, on the same go we could solve the similar problem of having only one RSS feed available for embedding. RSS is much reliable than scrapping the HTML source code (I believe it also could avoid the problem of topics created when users visit old pages, but that might be wrong and is secondary anyway).
@joebuhlig, as far as I can see, your recommendations doesn’t apply to our use case, because we have many external sites generating topics in different categories and with different usernames.