I remember they were meant to do it in 2021 but dropped out for the 2022 replacement version and were replaced by Muse. Which, given my attitude as a big Muse fan and Mumford disliker, I think you can guess I would see that as an improvement.
As said above, they did come back to do it in 2023. Dunno if that makes it too soon or that given The Killers did both 2022 & 2024 that they are the kind of festival to rebook an act twice in three years.
Wembley would be a surprise given they seem to already have a record number of shows there.
Tbf, Spurs, London Stadium, Twickenham and two nights at BST Hyde Park are still available AFAIK.
With it looking like TikTok is going to have to stop operations in the USA this weekend, makes you wonder what the actual trend will be for making pop hits happen when one considers that TikTok was going better in how it was working to attract young people's attention.