U2 have really protected us from true demos. Other than Desert for Your Love and Rise Up, most of their released demo recordings (Levitate, Where Did it All Go Wrong, Big Girls Are Best etc) have all been quite polished.
And they've kept in their lockers a bunch of songs we know exist: Mercy, Be There, Womanfish, Wild Irish Rose, Wanderer w/Bono, Mystery Girl w/Bono, other Clockwork Orange tracks etc. The fact that these have not been used as b-sides, remaster fillers or fan club releases is strange. But sadly it leads me to think we'll never hear them.
I'm not interested in seeing the quite raw Hansa recordings released, but they developed at least three of those tracks further when they got home to Dublin (Salome, Where Did it All Go Wrong & Lady With the Spinning Head) and decided not to put them on the album. I wonder how many other tracks (maybe Wake Up Dead Man, Woman/Sick for Love etc) developed further before being discarded (or reinvented). Now those would be interesting to hear.
I'm sure U2 could easily fill 4 or more CDs of demos & rarities, but I won't be holding my breath.