Using substack's 'ack' branch of hypercore, you can set an 'ack' flag to 'true' when creating a hypercore replication feed, and you'll be able to tell, for any given hypercore log block you append to a hypercore feed, whether it has been received by a peer.
As a test, I ran "node testsend.js" below ... which generates a public key [KEY], and allows me to type messages into the terminal 'live'. In another directory, I ran "node testreceive.js [KEY]" in order receive those messages ...
Here's what it looked like on the 'send' side as I typed in new messages (I'm including a snippet after I'd already been testing a while) ...
2019-07-06T23:03:14.746Z> bubbles