I don't think we've seen anything like the last of Boy Falls. Remember, they have been working on it for at least five years in relatively intact form, it was rehearsed literally every single day of the Ozzie rehearsals, (which hardly suggests dropping it) it's very specifically credited to U2- not just Bono and Edge, McGuinness cited it in an interview and Willie Williams says in his diaries; "The moment came and Bono announced “the next song we’ve never played before”. Edge began a moody guitar intro and perhaps the audience might have imagined that something acoustic might be about to follow, but when the whole band launched into Boy Falls From the Sky it practically took the roof off the stadium. They had rehearsed the song at soundcheck just using their onstage monitors, so this was the first time that any of us had heard this gigantic sound over the P.A. system (including Joe mixing the front of house sound, bless him). It was shockingly mega – out at the mix position we were all looking at each other going “…wow”. I don’t know where that song will go, but it’s absolutely epic."
So... if that was the reaction to its first outing and they rehearsed it non-stop before the next leg, I doubt we've seen the last of it. After all, HMTM is a Batman song! Miss Sarajevo is originally half performed by Pavarotti! They wrote the song, there's no reason for them not to play it.
I also query how you can say they want recognisable openers when the last openers have been Breathe and then Return of the Stingray Guitar....
Sure, i'll concede that they might want to play it. It's always
possible, i won't deny that. The favourable reaction from Willie and the guys and rehearsing it before the australasia shows suggests they like it, but the fact they
didn't play it speaks more to me.
However, that's not to say i'm not convinced it will never be played again. Just that it looks unlikely to me.
What i am pretty convinced of, is it's place as an opener. You might disagree, but i don't see this as a proper u2 song. It was only written by half the band, it's purpose was to be played during the spiderman musical, and it's not meant to be played by u2 in said musical. HMTMKMKM was played during the credits of batman, rather than the actual film (making it less of the actual 'soundtrack'), and it was released as a single by u2 (and composed by the whole band), and sure, HMTM and Miss Sarajevo have been played (which is great), but were they ever openers? I think BFFTS is much less connected to u2 than those two songs, so i think it has even less chance of being an opener.
I know your feelings on Stingray being a full song, so we'll have to agree to disagree about that - to me, u2 have been 'walking out' to stingray after space oddity, same as they 'walked out' to soon after space oddity, and i feel that Beautiful day has been the true opener. Even if i did think of stingray as a full song, and the proper opener, if they really weren't so determined to have a recognisable song that was
guaranteed to get the crowd rolling, they could have played Boots or No Line after stingray. The fact they went with beautiful day suggests to me that they really want the crowd to recognise the songs from the very beginning... or, at least from when Bono starts singing lyrics in whatever song they're playing

So yeah, that's my opinion - they've been opening with a well known staple, and i don't think they'd open with a lesser known song only written by half the band, intended for a musical.