I encounter more and more organizations or people who are collecting lists of feeds or blogs for one purpose or another. With BlogBridge we have the BlogBridge Topic Experts. Global Voices have their collection of international blogs (very cool!) And of course, anyone using a feed reader or aggregator has their own list of subscriptions.
Anyone who is making a list of blogs or feeds (or I suppose, URLs of any kind) that is not secret or private, would do well to record that in a simple OPML list. And the 'handle' to that list or collection is a URL.
Lets see. Instead of telling people, you can find my list of best restaurant blogs as a BlogLines list, or as this html page, or as a BlogBridge Guide, you refer to that list by the URL of the OPML.
It's a subtle shift: instead of thinking of OPML as a handy interchange format, start thinking of it as the most elemental format for representing a hierarchy on which all others are built.
(This insight is clearly inspired by Dave Winer's new OPML stuff, particularly the service which accepts and serves up OMPL files.)
Going on. If this is a good way to think about things, then this argues that the OPML service and format at its core should remain minimalist. That as people decide to layer other semantics (as they will and should) onto their lists and hierarchies, that these be kept separate or separable from the OPML. I am not sure where this leads.
I am just musing to myself (with all of you listening in.)