Krall of course is married to Elvis Costello, who collaborated with Paul earlier.
Frankly, I thought they would have made a real good team, Costello kind of provides that cynical side that John had with the Beatles.
Good point re: Paul writing with ElvisC - that certainly would have been interesting.
ConservativeDude - Paul has been a VERY underrated bass player. The Beatles early albums were engineered by Norman Smith who potted down the bass. It was only with Geoff Emerick that the bass became more clearly discernable.
As an aside, my fav bassist is Jaco Pastorius...and Paul certainly captures that same musicality in his bass playing.
Norman Smith, the Beatles and Pink Floyd:
http://www.soundonsound.com/sos/may08/articles/normansmith.htm