I've been talking about more OPML support in Drupal for quite some time. I'm here at Gnomedex, where Dave Winer is going to release his new OPML tool, and it seems like Microsoft is going to make some big announcement as well regarding extending RSS.
The latest from Dave indicates that he's got some interesting concepts about local, desktop editing of OPML files and then reflecting changes on your online website. This is very similar to what John VanDyk, Mathias, JonBob and I dreamed up for Mac OS X and Drupal in a beer cellar somewhere in Belgium.
I'd like to at the very least consider OPML to be a general format for import and export of blog posts between different tools. Of course, maybe we'll start seeing OPML chiclets appearing on web pages.
The Microsoft "lists" extension to RSS is somewhat troubling. Lists are kind of what OPML is all about. But, I'll withhold judgement until we know more.