I think in the past U2 wrote music that was inspired by other artists.
Their early 80's output was inspired by punk and postpunk outfits like Television and Joy Division.
Their UF period was inspired by Van Morrison, by Talking Heads, by Eno, and more otherwordly sounding music.
Their JT R&M period was inspired by the roots (not the rap group) - Dylan, gospel, blues, springsteen, Roy Orbison, etc.
AB and Zooropa was inspired by the alternative acts at the time, shoegazing, rave music, industrial, a tinge of grunge, and basically anything that was polar opposite of what U2 was laying down in the past (which the same could be said about their 2 previous periods)
POP was inspired by dance music, electronica, trance, triphop, while also introducing a more traditional approach to songwriting, with Oasis being a big influence.
ATYCLB was inspired by pop music, R&B, and also, for the first time, doing something they had strayed from in the past....being influenced by THEMSELVES.
This is where, IMO, things start to go wrong. U2 was at that point (subtly tho, mind u) trying to sound like U2.
BOMB is where I think they lost direction. It was U2 trying to write just that, a U2-sounding album.
NLOTH has some outside-the-box thinking, but unfortunately they couldn't resist writing those "U2 brand name" songs. Not only that, but (and remember this is my opinion) it sounds like they were tyring to recreate the BOMB era in those few tracks. You had NLOTH doing its own thing. Why were the flashbacks needed?
What I'm trying to say is: U2 doesn't need to make music that "sounds" like U2. We all know its U2. Play Zooropa's title track next to Beautiful Day, next to A Sort Of Homecoming, next to Acrobat. IT ALL SOUNDS LIKE THE "SPIRIT" OF U2!! All very different sounding songs, but they all sound inspired! Because that's what happens when you stop trying to push your sound, you start sounding like an uninspired cover version of yourselves.
Take the new Mercy. Maybe wasn't the greatest song from the get-go, but the original did have one thing going for it. That U2 sense of wonder! Tho you could argue the original is just U2 trying to sound like themselves, but the delivery and execution of it was something new. The extended verses, the outtro, the length of it. The bending of form and structure. The new version has stripped the song back to just the bare essentials, a concise "U2 sounding like U2 song". That's not enough, the song needed those weird twists and turns to pull off the trick. That would be a brave move for U2, to write and record some drifting, Astral Weeks inspired types of songs. But alas, it didn't go there.
To sum up, when U2 follow the sounds of their influences, whether they be old or modern, it comes out sounding like this: inspired U2.
When U2 tries to sound like themselves, it sounds like this: Coldplay (just kidding). It sounds like U2 on autopilot. No new surprises. It's not enough to sound like U2, they need the inspiration to go along with it.
Not sure this fits in with the discussion. But it was just a thought I had.
Out of the new songs, I hope EBW and North Star make the cut (with "new" sounding arrangements, not "U2" sounding arrangements). They will always sound like themselves, but they don't need to sound EXACTLY like themselves.