U2 will never have another album that will remain # 1 on billboard chart for consecutive weeks.Because the 16-24 years old music lovers don't care for a U2 new album.They'll buy a ticket to see them in concert because they are an event as a live act,just like the Rolling Stones,but that's it.
Listen to them around you...(meaning the 16-24 years old).So releasing a record in the spring or in the fall of 2013 won't change the perception of the non-u2 fans or music fans in general.
Sorry to discuss a bit more about charts and sales, but it all depends on U2's goal.
AB was released in the SoundScan era. AB spent just one week at #1. One week there, despite being one of the hottest artists around.
Some reasons for this are the sheer number of album that are released at that time of year. For example, ATYCLB had record SoundScan sales for U2 (at the time), yet it didn't even reach #1 (only #3) because of the competition.
If U2's goal is to have an album stay #1 for at least a few weeks, then later spring and summer seem to be the best times. Less albums are released and the competition is decreased.
However, if U2 wants that big burst of sales even if they aren't #1 for long, then November is still the perfect time. The holidays add substantially to an album's sales, even in this era of iTunes cherry-picking and illegal downloads. But U2 probably won't have an album that stays at #1 for more than a week.
U2's fan base is large enough to most likely ensure sales of over 400K in the first week in the U.S. But to increase upon that, U2 do need that big hit song that keeps the album going, like BD or "Vertigo".
If U2 just want to release good music and screw the charts/sales, then they should focus on what made parts of NLOTH really shine (it's the same parts that made JT shine). Songs that don't sound like hits or anything on the radio, but still succeed.