While I know the chances of this are none to zero, what I'd love to see from U2 is a true double album. I don't mean like R&H, I mean a true 22 to 24 track release. The first disc could contain the more "rocking" U2 - showcasing their next direction. The second disc could be the highly experimental U2 - which may or may not showcase their next direction, but allows them to explore ambient sounds or songs that may not typically be under the "U2" heading. In other words, "Songs of Ascent" could be that second disc.
U2 have never released a true double album and I think now is the time to do so. If 22-24 songs are too much for them, then make in 20 or so (10 songs per disc). But make it the best of the 5000 songs Bono says they have worked on. Songs that are great but risky - disc 2. Great rock songs that they put up against anything they've released in the past - disc 1. Of course, fans will always argue about which song belonged on what disc and perhaps a b-side should have been included as well - but that's part of the fun.
But even I don't think U2 are brave enough to show that much. Given where they are in their careers, I actually think now is the perfect time to do such an event - take that risk, prove to everyone you can rock and experiment; write pop while still creating great art.