On Maemo 4, the RSS Reader supports offline reading, and there are other third-party apps that you can use for reading RSS news, especially Feed Circuit, Nibbles and CloudReader.

From that I suspect offline reading of RSS feeds will be supported one way or another on Maemo 5, too. And if the official app does not support it, 3rd party apps will probably be ported/created sooner than later. With the feedhandler package that will be available soon, you will then be able to subscribe to a feed directly from the browser and select which app you want to use as RSS reader.