How have the band been building it up? It's 18 minutes long: people have asked about it; and one or two band members have talked about it. That's kinda all that's happened.
I'd say the fact that they singled that song out in the album's press release is a good start. With TFF, I seem to remember the band hyping up WWTWB for being the third longest song in the band's history and it promptly received a lot of media attention in reviews and interviews leading up to the album's release, much like what's been happening with Empire right now. Iron Maiden's epics are generally among their most praised and loved songs by the fans. Now they have a song that's five minutes longer than the previous longest song in their discography.
I'd love it if they did... but there would be a whole lot of additional instrumentation required- based on what we've read so far in Kerrang and TeamRock it sounds like there's quite a lot of piano and strings.
Plus, they'd have to whittle their setlist down by a handful of songs- or go out and do a double set with no opening act. Don't get me wrong, it would be absolutely amazing, I just don't think it's realistic.
That's true, but again, they can have the SSoaSS dude come up onstage with a piano/keyboard to play Bruce's piano parts and also pipe in the strings (if they wanted to). It's not at all unheard of.
Sure, but that didn't stop the band from playing the entirety of AMOLAD from start-to-finish on its album tour, when it was the then-longest album in the band's history. It's not blind desire that's motivating my thoughts here. I'm honestly more excited for If Eternity Should Fail than Empire. However, with all the hype the song's getting and its apparently theatrical sound in mind, I feel like this song is probably tailor-made for the band's live shows.
Granted, my thoughts might change once I hear the song, as it could turn out to be so musically complicated or fragile that it'd be too risky to play live (like Starblind or Alexander the Great). I don't think that's the case though, so I think the band will be willing to take out a regular song or two from the setlist to put Empire in there. Hell, they dropped
Hallowed Be Thy Name so that they could play Phantom of the Opera and Seventh Son of a Seventh Son on the last tour.