This would be wonderful! I actually offered Jeff (who pointed me to the topic) and Joel a few weeks ago to host a hub for them.
The Appspot hub is great, but it was built as a "demo" initially, even though it is now used by most of Google's properties.
However, I think the Superfeedr hosted hubs offer a few other cool features, like export of the data (that that appspot hub doesn't have), analytics, and a few other neat features that we're announcing soon. We already host hubs for the folks at Tumblr, Posterous, Gawker Media, HuffPost and several other publishers (big or small). I'd love to count the SO feeds as well!
Jader, there are actually 2 steps to making feeds realtime.
The first one (discovery) is roughly what you describe. (It's important for RSS feeds to add a link, with
The 2nd step is to ping the hub whenever a feed is updated. The hub will then fetch the feed, make diffs (to see the old vs. new entries), and notify subscribers (obviously!).
All in all, no matter how you decide to do it (Superfeedr or Google), I think this is a great step for the community and that will allow people to build interesting clients that can consumer the SO data out of SO. (who said IM bot?)