Mikal raises the best point. While we, the fanatics, want to hear a return of Hawkmoon 269 or would love to see Acrobat performed, the casual fan does NOT, and guess who makes up the majority of people at U2 shows! People attend U2 concerts because they want to hear their favourite hits, they want to hear the songs they hear on the radio, and these happen to be songs such as WOWY, Pride, and Mysterious Ways.
U2 have a hard job. Not only do they want to play the songs THEY enjoy playing, they also need to promote their new material, cater for the casual fan and the newcomer, provide the fanatics with the gems they want to hear, AND consider current abilities. I don't envy them. Those of you over on the New Tour Setlist forum or who read my LiveJournal will know I love designing U2 setlists - it's my passion and you'll often find me doing it. However, I adore eighties U2, and when I try to design something that will fulfill the criteria I just mentioned, I get very stuck.
Face it, even if they do rotating setlists, they will almost certainly only play singles or the non-single classics. That means Gloria might have a chance, but I Fall Down probably doesn't even enter their heads. We may see some songs return that haven't been played in 10-15 years - i.e. Running To Stand Still and When Love Comes To Town - but we probably won't see the rare gems unless there are very special circumstances (such as a concert in New Zealand, where One Tree Hill will be played).
There is this talk of rotating setlists, and I foresee two possibilities.
1. A more pronounced version of Bad/AIWIY from Elevation. One night, we could see Bad/Streets/Pride, the next Stay/ISHFWILF/AIWIY, the next Bad/ISHFWILF/Pride.
2. U2 have enough classic and new material to create a 30-40 song setlist. Split it in two, exchange some common elements (i.e. make sure both have Streets and a couple of recent big hit singles), throw in a few old gems that are occasionally rotated (i.e. I Will Follow most nights, but sometimes Out Of Control or 11 O'clock Tick Tock), and there's your multiple, alternating setlists.
I really could go on about this forever.