I'm guessing late 2015 early 2016 release. Now that they've really dug their heels into the new lineup with ADTOE and DT12, I feel like they might go a little outside their recent creativity bubble with the next album. Hopefully. There's no telling, but that would be ideal. More of the same at this point wouldn't be too great.
I know they said in an interview at some point that they hadn't done a concept album in a while and that it would be cool to do one (idk if they specifically said that last part though, it might've been worded differently). If they're willing to do something different and be creative with it, a DT13 concept album could be possible. Again, hopeful thinking...
At least something different than 5-7 minute prog-metal rockers. I've said before I think DT shines with their 8-15ish minute stuff, and if they could be a little experimental then all the better. Something like how SDOIT was when it was released. Like it was said earlier in the thread, it probably won't be DT's "Heritage"... Dream Theater will be Dream Theater. But I'm hoping for Dream Theater with a twist here and there.