Both Eric Clapton and Neil Young have done exactly this before. I remember my parents went to see Clapton 15 years ago when he did his From The Cradle album and tour, and the concert was ONLY the songs from that album. For those who haven't heard it before, it's what I'd affectionately call 'old black man blues'
. Imagine going to a concert expecting to hear Layla and Lay Down Sally, and getting that instead. But the thing was, EVERYONE loved it! My parents came home and immediately bought the album, and have worn it out ever since. They just don't buy new music either, so the concert must have REALLY impressed them. They still talk about that concert to this day 15 years later, and they've seen pretty much every major act out there. Fleetwood Mac really could do this. I seriously doubt they will... but crazier things have happened.