A tweet with cryptic text was posted to the Twitter account on December 31, 2017 at 6:39 PM EST. (This was four days after ♐REVI was posted to the twitter account.) Decoding this lead to the discovery of of the 3rd youtube channel.
The text of the tweet is:
The symbol ⌅ can be used to mean Projective space.
It was discovered by discord user Peter that the text string is encoded in base64, which decodes to the string”UCsgRTRJNy05MuB7g2X5ueqg”. That string of characters appears in the address of the 3rd youtube channel.