I'm assuming that the next album will be more 'music' focused - as opposed to The Astonishing, which was more 'history' focused (although it's pretty obvious they experimented with many genres in The Astonishing as well). Like some other forum members have said, we might get that 'world music' album.
Either that, or they'll do a simpler, fun rock/metal album - kind of what they did for Systematic Chaos. I see many parallels between The Astonishing and Octavarium (both feature orchestra and shorter songs, both focus on some sort of concept), so maybe the band will approach the next album the same way they did in 2006.
Maybe a punk album with all songs in 4/4?