Would be the right move to do in 2001 when they were huge and pretty much universally loved.
On the last two tours though, there's been collateral damage via Bono's activism/speeches...
You mean in terms of general public perception? I agree, ATYCLB era would have been very good timing. If HTDAAB had been the original back-to-basics "four guys in a room" album, that would have been a good time for it as well, musically. This does wreak of a bit of a forced campaign type of thing, an awareness that they've lost ground with the 'music' music fan over the past decade, and that U2 are seen as a larger monster beyond the songs - extravagant touring, extravagant Bono etc - as well as a bit of a dinosaur band, and perhaps this is a too obvious attempt to rectify that.
Still, it presents a great challenge and great opportunity. My biggest fear is really that they just come out flat, or off, for some reason that they can't overcome, e.g. if Bono's voice has one of those nights. Shit happens, and it's a fairly punishing schedule.
The performance and the setlist are crucial.
Simplistic performance and stage show for the most part, but with one eye on Muse the following night (who will go nuts on theatrics), so some techno-showing off, but maybe for just a run of songs. Maybe present newer songs in a minimalist way, and give the run-of-classics an all out show, as no-one doubts the strength of those songs on their own.
Setlist wise, I know they won't pull anything unusual out of a hat. It will be pretty much the 360 setlist, and if anything 'new' is to come up, it won't be that weird, perhaps just something that has been rested a lot on 360 but heavily used previously. And either way, whatever it is, it will no doubt appear in 360 gigs leading in, or at the very least we'll hear about it being rehearsed at sound checks. There'll be no surprises for U2 fans.
But I do think they need a different order to the setlist, to the usual 360 placement. U2 fans want classics and new juggled pretty well evenly, not too much of a run of either, and are okay with the front end of the set being newer song loaded. I think at Glastonbury, there will be a couple of times where they'll need to knock it out of the park, grab the crowd by the neck and shake them furiously, and I think the opening run of songs will absolutely be one of those points. Probably the most important. I don't think they should come out with mostly new songs up front, even if they are 'lively' songs. Don't think they should open with something from No Line. I think they should go for a blistering opening, even with one of the big classic songs appearing up front, within the first two or three songs. I think that in at least two spots on the set list, they should be effectively beating the crowd over the head with "We. Are. U. Fucking. 2." The opening is one of those, and a latter third blistering run would be another. At both points, it's no time to push relatively unknown newer songs.
My random pick to actually open the whole thing? Until the End of the World. Never fails live, they never fail to lift that song, it's not a warhorse (to the general public), it opens up brilliantly, it's a show off song, and it's a great Glastonbury fit. Back it up by an immediate one-two punch of two relatively energetic songs, with at least one of them being regarded as a classic or seriously well known U2 song, and you're off to a great start. Opening with some mix of Breathe/Boots/No Line/Magnificent - for this crowd that would be coming out VERY slow off the blocks, IMO.
A very delicate balance between old and new, and recognising that this is not an opportunity to make an argument for the 00s or a showcase of No Line, are really the key though.