I have to shake my head when I read comments from Dyer (and others) saying that John Coltrane had reached a dead end in his music. Some even are even foolish enough to speculate where Trane's music might have evolved. Music, like any art, is an ongoing process, and that results of that process might be a mystery even to the creators. I wonder whether John Coltrane had any idea where his music would be in ten years when he was playing with Miles in 1956. In early 1967, he may have had no idea where his music might go.
John Coltrane kept searching until the end of his life and his music is there for us to hear. All we can do is listen and take whatever we can from what he offered us. For Dyer (or anyone, for that matter) to say that Coltrane had reached a dead end in his music is presumptuous at best, and ignorant at worst.