If they do a past reunion epic, I think it'll be something from the last two albums, most likely TFF. I could see them dusting off FTGGOG or When the Wild Wind Blows. Both should be somewhat easy to pull off. DoD seems like an easy guess just because they did it on the last album tour, but remember that was the first time they played it since the DOTR tour, so it's not exactly a staple. I'm pretty sure they'll give it a break this time.
I haven't heard the new album yet, but both TBOS and Red and Black seem like a given. I don't think EOTC is totally out of the question, especially if they notice the overwhelming response that it's getting I can't imagine them not at least attempting it. However, those three songs plus If Eternity Should Fail and another epic make up almost an hour of set time. I hope they do a 00s focused set plus maybe 4 classics (Fear, Hallowed, Iron Maiden, NotB ) so that they can play all those epics and give the new album proper attention. Second leg of TFF was a disappointment in that respect.