The pledge idea sounds fine enough for struggling artists, I suppose, but I don't see anyone as successful as U2 doing that, or needing to.
And no, the app (if it ever comes to pass) certainly won't be the sole version of the album--and I might guess won't be terribly significant in terms of how the album should even be experienced, if at all. It would be too limiting for those who don't have an i-device. Was the Corbjin movie associated with NLOTH (I forget the name) ever viewed as the "essential" way to listen to it? I'm honestly asking--I've never seen it, and rarely heard it referenced.
I don't think anyone would expect U2 to go down the Pledge route. But it is an example of smaller artists embracing new technology, something that bigger bands like U2 have been slow to do. Reimagining the album format as an app sounds like U2's attempt to use the new tools at their disposal to present their music.
I guess the idea of Linear was to create a video version of the album that was mainly designed to be viewed on portable devices. It was an interesting attempt, but ultimately wasn't very successful. It probably worked better with the earlier version of the album that it was filmed for.