I wonder if the notification digests via email are now incorporated into CB activity.

This won't be happening until CB 3.x as we need an entirely new API layer for emails. We need an email queue system, email batching system, and an email digest system. The queue lets us schedule non-priority emails, the batching lets us send those emails in reasonable batches (e.g. 100/day), and the digest system lets us group emails together based off recipient (e.g. user has 3 emails queued then group them into 1). This will all be generalized in core CB so all our plugins can utilize it.

If not, is it still planned?

Yes, it's still planned.