Today I read an interview with Bruce in Aardschok (Dutch metal mag) and thought this was an interesting part (and a good question* nowhere else asked):
Bruce on "If Eternity Should Fail":
In the summer of 2014, at the end of our last tour, I let Steve Harris hear a demo of a song meant for my next solo album. That was If Eternity Should Fail. It even was the intended title number of the intended album. The lyrics are about a machine which steals the soul of humans. Steve was enthusiastic immediately: "That's the perfect opener for the next Maiden record!" And so it happened. Pieces of that demo have survived by the way. The instrumental beginning I have recorded in the bedroom of Roy Z, producer of my solo records
*Are the interests of the band always more important than the ones of your solo career?
No, if I could keep it for myself -that's mine,, mine, mine!-, it wouldn't have been a problem at all. At the end, it is my song. By the way, I am still planning to use my version on my next solo album. This way, the audience can compare both versions.