There are definitely a few of us that use SilverBullet for tasks, but I’m not sure how many are using it as their only todo app.
If you haven’t already, take a look at these threads for inspiration:
I think the biggest missing feature is what you already mentioned, notifications. It should be possible to add some sort of notifications using space-script or at least in a plug, but I haven’t seen anyone do that yet other than the ICS integration in one of those threads.