Some great questions here.
The original contract for the compilations was a separate contract sitting on top of their existing one. It was for three compilation albums to be produced over a 10 year period. They did "The Best of 1980 - 1990," "The Best of 1990 - 2000," and "18 Singles" which fulfilled that particular compilation. I'm not sure we will ever see a "The Best of 2000 - 2010" as there is so little content there. Most of the ATYCLB singles ended up on 1990 - 2000. That leaves HTDAAB and NLOTH, and they don't seem to be in any hurry to revisit NLOTH. That being said they could certainly do another compilation like 18 Singles, revisiting some of the more recent music. A compilation that includes the songs from the more recent albums as well as a few earlier hits to make it interesting to people...but they are not under contract to do one currently that I'm aware of.
The Joshua Tree video will be released. The sound was mixed last summer for the release, and will feature the concerts from Mexico, as well as some footage from San Diego. Originally we were told to expect this one before Christmas but it looks like they are now looking at early Spring for a release instead. And, if you believe Anton, it will get a limited run in theatres as well! They have also filmed Washington DC, and will be filming Berlin for a E+I home video release. They are hoping to use the Berlin footage from what I understand, feeling that the Washington video may feel too much like the earlier video with the same stage, same songs, and same videos even. They also have done some filming with 360 cameras - capturing the performance at Newark and at the Apollo Theatre. That footage should show up somewhere down the road I'm told.
Remaster of Rattle and Hum...the remastering group that worked on the early remasters - Boy through Achtung Baby - was dismantled. The more recent Joshua Tree box set wasn't done by the same group, nor have the vinyl releases. I'm told that originally there were some plans for a bit of a celebration of Rattle and Hum this fall that have since been decided not to happen. Part of that would have seen a new version of the album on vinyl, which has now been pushed back. There was no plans for a box set like other albums I'm afraid - just the vinyl. The Paramount issue as I understand it is that the band is only allowed to reissue the album, they can tweak the audio, they can release it on super sparkly coloured vinyl, they can hand sign every edition, but they can't alter the album substantially, i.e. they can't add new tracks.
Songs of Ascent? I spoke to Danny Lanois about this one direct. He said the album is there and could be released tomorrow. The only song that has been taken from it is "Every Breaking Wave" but it could be released otherwise. But the band have seemed to back off from talking about it. They seemed to want to release it / work on it...but it may be a while before we see it if they have newer ideas they want to pursue.