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The Grateful Dead’s farewell continues to grow. After initially announcing three July shows in Chicago, the band responded to high demand by adding two June concerts in the Bay Area—and then tacked on special movie theater streaming of the gigs, as well as pay-per-vew broadcasting of the events. Now, Billboard speculates that the five shows might not be the last for the “Core Four” surviving members of the Dead.

According to a Billboard report, multiple sources confirm that the band is planning a fall tour that would start in October and feature John Mayer. Although a rep for the Dead told Billboard such speculation was premature, there’s legitimate precedent. The “Core Four”—guitarist and singer Bob Weir, bassist Phil Lesh, and drummers Mickey Hart and Bill Kreutzmann—already proved their willingness to add Dead outsiders into the mix when they recruited Phish’s Trey Anastasio to play with them at their final Bay Area and Chicago shows. Weir also jammed with Mayer when the 37-year-old hosted the Late Late Show back in February.

Lots of money hangs in the balance when it comes to a potential tour. Billboard estimates that the five already-scheduled shows have generated $50 million from ticket sales alone, and that demand indicates the band could’ve sold six million more seats.