Whilst I think grand departures are pretty much off the table at this point, there are one or two simple things the band could do that would at least make it appear as though they are making a break with the past to recapture some attention.
Like changing the way they look.
The bands image has been all but identical for about 15 years now, a world away from the band of the 80's and 90's, whose aesthetic was constantly in flux, every album had a its own visual identity.
Image is everything in the music industry and its a hell of a lot easier to create the impression of change, rather than actually changing anything at a fundamental level.
As most people only ever focus on the frontman, he is the one that has to be seen to be changing most radically. Just take a look at a band like Queen, Freddie Mercury's image altered dramatically through the years, creating the impression of multiple incarnations even when the music stayed pretty much exactly the same. It didn't matter that his fellow band members never followed his example, his ever-changing identity was enough to keep people engaged.
Bono could lose the shades and jacket and try something different. The music staying the same is one thing, but when the image stays the same as well it just compounds matters and people simply presume they've seen in all before.
They also wouldn't have to necessarily overhaul their sound either, part of the problem with the more recent material is that an awful lot of it is a bit too sanitised. But something that touches a nerve in the listenership, that confronts them with something they're a little uncomfortable with might make the tune lodge a bit longer in the brain than its 3 minute duration.
ZOO TV had vaguely controversial connotations and could occasionally challenge the audience with something deeply uncomfortable. It made the work stand out all the more amid the glut of mainstream music. Maybe the band could try something like this again.
Anything that creates an impression and gets people interested in the band again (and that's what I think is missing, people just don't seem very interested in U2 right now ) is exactly the kind of thing they need at this point.
