I really hope they do this. It would be massive. There's a lot of people out there that have the wrong impression of Fleetwood Mac. I honestly feel they could blow people away- the potential to be one the most legendary Glastonbury headline slots ever. I think they could even get 4 albums into the top 20 on the back of it (Rumours, Very Best of, Greatest Hits, new album) and the potential for a return to number 1.
A mini blues set half way through featuring Peter and Jeremy (with Lindsey) would top it off.
...but I'm not sure I can see Fleetwood Mac doing it.