Not expecting anything, but since World Slavery Tour 84/85 was their biggest and most succesful, it would make sense to release something from it this year or next.
Within the still relatively far fetched realms of possibility would probably be "new" material from the Long Beach Arena gigs (I believe they used mainly material from nights 2 and 4, so something from 1 & 3), soundboard audio from Rock In Rio or one of the four Hammersmith gigs with either or both hd footage and soundboard audio.
Then less likely scenario, maybe more live material from Behind the Iron Curtain, something from the five New York gigs (as noted in the cover booklet, only illness prevented them from being seven), or just from a random show which has not been released previously.
If they however release something, its probably going to be something else. But not "rarer stuff" than this if you like, that´s for sure haha.