If you remember, I brought out that in Mark 9 the first verse seems to maybe be out of place. I think that the first verse of Mark 9 is the reason why there is no account of the transfiguration in John. I believe that John took that word from Jesus for himself. "I assure you that some of you standing here right now will not die before you see the Kingdom of God arrive in great power." John describes himself as the one who Jesus loved. I think that John had a relationship with Christ that the others did not. He accepted Christ without reservation, and he believed that he would see the Kingdom come. And he did--check out The Revelation. In John's Gospel Chapter 1, He says this(verse 14)"So the Word became human and lived here on earth among us. He was full of unfailing love and faithfulness. And we have seen his glory, the glory of the only Son of the Father."
John was talking about the transfiguration. He did not give an account in his Gospel because he believed that he would see the Revelation before he died---and he did---be blessed---c