Hi Kovid, Fem and others here in this thread,
It's very cool to see that you integrated Fem's plug-in into the core build of Calibre. OPML is much under discussion at the moment. The current approach of offering an import function unfortunately results in a static copy of that OPML file. I propose supporting remotely hosted OPML reading lists. These could be reading lists on someone's own website, on a feed reader's website, or even on a cloud service.
A few weeks I wrote an in-depth article about this topic that you may find of interest. It offers an introduction into the issues and then explains how one RSS feed reader, InoReader, resolved them:
RSS Reader InoReader to Support Dynamic OPML Subscriptions, by Marjolein Hoekstra (@CleverClogs)
Marjolein Hoekstra
@CleverClogs