Look, I don't think Coldplay will return to rock, I think it will be a Space Pop album, with several songs in the style of A Head Full of Dreams and Mylo Xyloto
Everyday Life has not been a success and Coldplay needs a success at the level of MX and AHFOD to remain relevant and obviously also due to pressure from their label they will return to Pop but with a spatial theme, and also Rock is practically dead and not sell as it does the Pop