I am assuming as it's title is a bit outdated - as there have been a number of things released by U2 since 2004. Not that THE COMPLETE U2 had everything in every form to begin with but...
Since THE COMPLETE U2 release in 2004, U2 has released:
These singles (and their associated B-Sides:
2005 All Because of You [Canada]
2005 Sometimes You Can't Make it On Your Own
2005 City of Blinding Lights
2005 All Because of You [Europe / Australia / Japan]
2005 One [With Mary J. Blige] - Although not an official U2 release.
2006 The Saints are Coming [With Green Day]
2006 Window in the Skies
Plus the following albums:
2006 18 Singles
2007 The Joshua Tree [20th Anniversary Edition]
Being that all the singles have B-Sides, live tracks etc... and the 20th Anniversary has JT era single B-Sides and outtakes...
Needless to say THE COMPLETE U2 is hardly COMPLETE without all of this material added.
The question is
A) Will the offer it up with all of this material + the new album, when it comes out?
B) Will those that did shell out the 150-ish be able to buy the 'extra' items added to the set? (Probably not, as ALBUM ONLY seems to be the modus operandi for added or bonus material to most iTunes releases.