I am changing my mind about this topic. After researching the Twelfth album and the Black Album I can see that people have already attempted to re-unite the Beatles by way of combining their solo songs into imaginary albums.
As of now, I don't think this is a valid concept anymore. The combined solo stuff doesn't cut it for me. These do not sound like Beatles albums. I think that no matter how much you play around with it, it's not going to work. They needed to be together as a group in order to be The Beatles. So, I think John was wrong about his idea of having other Beatles albums by simply combining their solo songs.
As I type this post, I am listening to "The Twelfth Album" on YouTube. Note that it contains 12 songs and that it was named "God" by the Beatles (according to fictional account). Yes, somebody took the time out to assemble this imaginary album. Also, these songs don't seem to follow each other or connect with each other in terms of theme and mood. Here's what's on that album in numerical order:
SIDE 1:
1) Gimmee some truth (John) 3:19
2) It don't come easy (Ringo) 3:05
3) Every night (Paul) 2:31 Not included on the YouTube album
4) All things must pass (George) 3:47
5) Child of nature (John) 4:18
6) The back seat of my car (Paul) 4:31
SIDE 2:
1) Instant karma (John) 3:23
2) Isn't it a pity (George) 7:11 I don't think the Beatles would have allowed Pity to be so long
3) Junk (Paul) 1:56
4) Wah-wah (George) 5:38
5) God (John) 4:13
6) Maybe I'm amazed (Paul) 3:53