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If he plays BST this time around (as he's done several times before) he pretty much is at Stevie Wonder sort of level.

Neither.  With the volume of recorded music available and the number of ways to consume it, entirely feasible you'd have missed something!   Having said that, I would suggest playing either Heart of Gold or Rocking In The Free World to see if they ring a bell at all.

Get Jack White in the slot below Neil, would be a perfect fit

There isn’t a “ "Macca/Elton/Madonna or Stevie (oof)" slot”  though. They’ve just booked Neil Young to do Neil Young things. Given the festival has had him play before, had booked him before that, and he’s been around for a very long time I’m pretty sure they know who Neil Young is and that he isn’t going to do what those acts do.    

He occasionally uses Shakey Deal as a pseudonym, so it's wound up as his nickname.