Live Nation has confirmed that U2 will not have an opening act for the Innocence + Experience tour. It will be "an evening with U2" and only U2.
While there have been scattered shows over the years without an opening act, it's the first major U2 tour (arenas or larger) ever without an opening act.
The last time they did anything like this was the end of the War tour. The Hawaii show had Oingo Boingo, but there were no openers for any of the others. The Japan shows were in small venues, however, not major arenas.
So plan to be there on time -- no opening-act cushion!