I think it would be cool if b2evolution could have the ability to automatically e-mail people on a list (kind of like an e-mail list) blog entries from a blog in which it is enabled. Options could include e-mailing people on the list once a day with all of the blog entries, or simply e-mailing blog entries one-by-one to people.
I don't know if it should go to all members, because not all members of a blog would always want them e-mailed.
I don't know how practical this is. Just throwing it out there.
The forthcoming "Phoenix" version of b2evolution will include email subscriptions. But b2evo already supports a feature that does a much better job of letting readers know when there are new posts (and comments): RSS.