An acoustical album by John and Paul. Had John lived and he and Paul reconciled their differences, perhaps one day they could have done an album together - just the two of them - in tribute to the magic they created as the Beatles. It was those two whose partnership and alchemy created the greatest band in pop music history.
It can never be and perhaps never would have been even if John still lived. I think it would have been psychologically impossible for John to agree to this.
BTW, this fantasy album could simply have been titled "John and Paul."
