Aside from the songs on Black Clouds and ADTOE which obviously haven't been on DVDs yet, what songs from the DT discography are you thinking really need a solid DVD release?
I'll work backwards:
These Walls: One of my favorite songs from Octavarium, and unfortunately I think the only performance of it is on that Romavarium fanclub DVD.
Blind Faith: The performance on CiM is just really lackluster for a number of reasons. I'd like to see this professionally done since it's one of Dream Theater's best songs.
The Glass Prison: The Bucharest version is really good, but obviously the audio and video could be a lot better.
Lines in the Sand: Same with Blind Faith, really. The CiM performances just don't cut it.
Caught in a Web: The live performances of this song have been killer lately, and as far as I know the song is only on one of the Bootleg DVDs.
Pull Me Under: The Live in Tokyo version is really good, but considering how it's the bands biggest hit and all it's a surprise a more professional version hasn't been released. Budokan's Pull Me Under has tons of problems, ranging from James' voice sounding thin and flat to the new "warped" arrangement that doesn't really work IMO.
So if these songs appear on the new DVD with my new favorites, like BITS, BTS, and TCoT, I'll be pretty happy.
Honestly, I don't really care to see any Systematic Chaos tunes. Not many of the performances of them on CiM are very good, but neither are the songs IMO. I'm guessing TDEN at least will make the cut, which I'm OK with. It's a fun song.