This is something that I think is really needed at the core level...

Allowing users to subscribe to content changes, whatever the module.

I know there's no way of doing this at the moment, unless I'm missing something major. I know modules can use the ISearchable (I think) stuff, that makes the scheduler search the content and return to the search results. What if there was an ISubscribe class which then lets a scheduler monitor DB tables? Users could be inserted into a table with the ModuleID and the Subscription scheduler could fire out templated emails with the Module updates.

I have no idea if this is possible, or if there is anything being done in the core to allow users to subscribe to data updates.

Anyway, just a thought.