I agree that he heralds were gaining extra abilities that Honor didn't intend or expect, but I think thats separate from the Bondsmiths connecting with the Old magic Gods because the heralds never gained one another's surges that we're aware of.
the context from the convo that gave me this idea pretty much states that the Stormfather replaced the Wind, The Sibling replaced the Stones, and the Nightwatcher replaced The Night for taking Bondsmiths. The three forces that Adonalsium left on Roshar before the shattering.
This scene also made me think that Nale's Spren broke their bond and left. The High spren also have very distinct looks that should be pretty recognizable. The other figure would most likely be The Wind since it doesn't look like an High Spren. I was wrong earlier about there being two people with blue skin in Renarin's vision tho, thank you for catching that.