Angel Eyes on YouTube shared these two incredible videos where he isolated the harmonies on Super Trouper and Knowing Me, Knowing You where Bjorn and/or Benny can very clearly be heard harmonizing with Agnetha and Frida in the background, and it's amazing.
I posted a while back I think, asking if Bjorn and Benny will be recording any vocals on the new songs, and it turns out I was right. Ice The Site shared a video on Instagram where Benny was asked the question, and Benny says that he and Bjorn are certainly on "I Still Have Faith In You." This makes me even more excited to know that when the new songs will eventually be released, we won't just be hearing Agnetha and Frida's incredible voices together again, but Bjorn and Benny's voices mixed in as well!
However long it takes for the new songs to be released, I'll be waiting and when the time comes that we get to hear ABBA's new songs, I know we won't be disappointed. :)