I just added a few things to Topicalla. I put together a simple script to read and convert RSS0.9/RSS2.0 and subscription lists in OPML. Selecting an item in the OPML view opens the corresponding RSS. Of course, it will also work no matter what kind of content it is -- if the URL pointed to by the OPML turns out to be FOAF instead, it will be displayed as such.
I also made the customize window do something useful. One can now add, modify and remove UI associated with particular types of content. For example, given a musician (which has an RDFS class of http://musicbrainz.org/mm/mm-2.1#Artist), I might add some UI which presents the list of albums created by that artist. This works, although I had to pull from a local RDF file, since the MusicBrainz RDF doesn't seem to contain a lot of useful info.
In addition, one can add additional datasources for a type. That means that I can load data from MusicBrainz and from somewhere else -- for example, a source containing music reviews -- whenever I display an artist.
Next, I plan to add the ability to add support for any kind of content.