It's funny that we've had Steve Lillywhite and Brian Eno, both having produced U2. Rick Rubin is an interesting choice, as he's produced so many different stlyles you couldn't say 'that sounds like a Rick Rubin record'. And you would need someone of very strong character, otherwise they'd be walked all over, and the whole thing would end in chaos. Jeff Lynne is probably the obvious choice having been a successful musician in his own right, they would respect and listen to him.