Depending on how many more albums and tours they have left in them, I think they will probably rotate as many songs from The Astonishing as they can in the future. But maybe they will play at least three or four songs from it on the follow-up tour, or the one after.
As for next year being the 20th anniversary of FII...it will also be the 25th for I&W, the 15th for 6DoiT, and the 10th for SC. Maybe they'll do a tour where they play two or three songs from each of those albums, at least one or two each from ADToE and DT12, and then fill the rest of the time with music from The Astonishing.
Also, I'm wondering if the "Astonishing Live" show is going to be JUST the album, which means not more than about 2 hrs. & 20 min., or if they are going to pad it out with some solos and/or other songs, or if they're going to have an OPENING act. MY guess would be a 15-20 minute (or longer) encore of at least a couple of older songs, or maybe something like ACoS, 8VM, TCoT, or IL