In case you haven't seen, User:Rillke on Commons has implemented a
(default-on!) gadget that makes it possible to subscribe to
notifications of different types, e.g. policy changes, new features,
etc. These are shown as watchlist banners and upon login.
Here's a screenshot of the "subscription" interface:
IMO that type of gadget lends supports to the notion of shooting for a
subscription model to be ultimately integrated with Echo so that users
can get standard read-once notifications about things they care about
while keeping the core UI clutter-free.