I'll believe it when I see it. Infinite Dreams is a song they've willfully ignored for 37 years, and it's a photography book we're talking about. A cool item no doubt, but not a terribly big deal in the grand scheme of Maiden releases. I see it as another part of the 50th celebration, not necessarily tour-related.
But, I said damn near the same thing about the chances of Caught Somewhere in Time showing up on the Future Past tour, so maybe my skepticism is a good sign that they'll surprise us again. I'm just doubtful at this point because of how long it's been shelved, especially on a certain 2014 tour that was supposedly dedicated to the one tour they played it live.