Revolution 9 was supposed to be an extended ending to revolution, but what it ended up being is a result of what happens when Yoko Ono gets involved.
Oh No It's Yoko!
Over and above introducing John to the avant garde, Yoko's input to the track is fairly minimal - it's primarily a Lennon / Harrison piece (although credited to Lennon / McCartney, it would seem 'Macca' had nothing to do with it). The Beatles were laready using musique concrete techniques (eg the instrumental break on "Being for the Benefit of mr Kite") and it would be fair to say that this was a logical development of that. In addition, George was into more experimental stuff; as well as his "Wonderwall" and "Electronic Sounds" albums, he introduced the Moog synth to Beatles music on "Abbey Road".
If you like "Revolution 9", you should also check out Lennon's first 3 albums; "Two Virgins", "Life with the Lions" and "Wedding Album" which take the ideas even further.