After landing Paul McCartney and Elton John in back-to-back years, what will Bonnaroo do for an encore?In talking with promoters on the 700-acre festival grounds Wednesday, they say plenty of star power still remains for the Bonnaroo lineup in years to come.“Some of the obvious legendary bands we haven’t gotten yet are The Rolling Stones and U2,” said Bonnaroo co-creator Rick Farman of Superfly. “We’ve had a lot of our heroes play here already, but those two really jump out as bands we would love to have. Getting some members of Pink Floyd here would also be nice.”Farman says booking acts for Bonnaroo takes place year-round with no starting or stopping point.“In some cases with your major bands, it’s a multi-year process,” said Farman.