If I had to guess and based on a few rumours:Not on the Pyramid, of course. Just responding to Sisco's message about Smith being offered for the Other, and the comments below saying it would be too big for that. I think that will probably be fine.
If Madge, Styles, and Fender are the headliners, Smith fits right in as the Other Head. It does become a fairly un-rocky quartet, though (knowing that Robbie W. is also in the picture).
Pyramid Headliners - Fender, Harry, Madonna
Pyramid Legend - Robbie
Other Headliners - Sam Smith, Phoebe Bridgers, Bicep
(Can’t wait to find 7 out of 7 are wrong