(Of course this is all speculation)
I think that Bono will have more influence on this album than the previous one. So, we'll probably get to hear a few of those acoustic songs he's been talking about (maybe 1 or 2). Too many people have already heard "Mercy" in its original form. If it shows up on the album, it'll be so re-worked that everyone who loved it before will be very disappointed. Sadly, we'll probably get the typical (as of late) 3-5 actual "Rock" songs. I think everything will be more experimental, but only as much as they feel safe with. That means nothing as bold and drastic as their 90's material, but some toying around with time signatures/instrumentation/etc.
I'll even go so far as to lay out what the tracks might look like:
1. Rock song = First single that gets people drooling for more, has a strong and heavy feel to it (Somewhere between Vertigo and Discotheque). New guitar sounds, but everyone still knows it's U2.
2. Acoustic Ballad = Bono tries to "fill the space" with his voice. Edge plays acoustic guitar, maybe a little piano or strings thrown in to highten the emotion.
3. Ballad/Almost Rocker = The next step in the "Beautiful Day"..."Miracle Drug"...evolution process (To me, those songs are similar). Maybe a little Beatle-esque horn section for something different.
4. Another Rocker like track 1 = structured like no other U2 song out there. We won't get the usual verse/chorus/verse/chorus/bridge/chorus style on this one and maybe it'll be a little more electronic. Experimental song that shows up in the middle of album to hide it in case it gets unwelcome reception.
5. Mercy reborn = Newly reworked to the point of almost becoming a ballad. Still a grand feel and the one song to really remind people this is a U2 record. Carries signature U2 sounds throughout.
6. Pop/Rock song = simple construction. Easily pleases with a fast pace and some power chord structuring.
7. Acoustic Ballad #2 = Bono's second go at carrying a song with his voice and not much else. This one will have a little more rhythm section still in it than track 2. Maybe we'll get a nice Edge harmony.
8. Experimental Song = Very atmospheric (Eno returns to the studio). Distorted drums and guitar. Many people will claim it's the weakest song on the album.
9. Last Rock Song = Bono squeezes in his one "with a cause" song. Some clever symbolism for the state of the world, but this time a more up-beat song. More like Sunday Bloody Sunday, less like Crumbs.
10. Rock Ballad = Slow start. Builds until the end. Classic Edge guitar sounds overlayed with piano.
11. Grand Melody Finale = U2's effort at an "Abbey Road" style finish. Maybe The biggest of their grand melody songs complete with orchestra.