Nothing that requires a full computer hooked up to the TV will ever be popular outside of geeks.
Plex, which started as a simple port of XBMC for Mac, has morphed into a much more impressive architecture. They separated the media management into a server component allowing different clients to consume it, including Mac (seems a Windows port is coming), iOS, and soon, LG TVs and Blu-ray players. You can read the developer's vision for it here:
http://elan.plexapp.com/2010/09/02/plex-and-the-future-of-television