Bob Weir

@stuartk - after Brent died, I was hoping that the GD could lure Bill Payne away from Little Feat; he would have fit in great, I think. 

@larsman 

Chops would not be an issue. Whether Payne could hang with the Dead's aesthetic is, for me, not nearly so clear. 

Of course, Garcia did manage to nab Nicky Hopkins for awhile. That would've been fun to see, in person. 

@stuartk 

Billy Payne did play with Phil & Friends on the Fall '99 and Summer 2000 tours.

The Dead had Bruce Hornsby in the guest seat for a time. His musical chops, ability to fit into the Dead's sound contributed to a brief musical renaissance for the band. Ultimately, he chose not to continue with them because of the vibe around Jerry's drug use.

@ezwind 

Well then, he clearly had no such reservations!

@wharfy 

Yes; I was aware of that but I've never heard any of those shows so I have no idea regarding Hornsby's stylistic versatility. 

Another great keyboard player: Reese Wynans. His work with SRV was stellar. He was for a brief time, the original Allman Brothers keyboard player but had to bow out to make room for Gregg.