Bruce had a wider range in the 80s, but much less control, finesse, power and technique. Today, I'd wager he has about 90% of his range still, while having more power, more technique, a thicker voice, and more control. The big issue nowadays (and I've said this before) isn't Bruce's ability to hit high-notes. He hits high-notes just fine. It's his wind. You'll never again hear Bruce belt out a 30+ second long note like he does on Hallowed By Thy Name from Rock in Rio. This has been the case, i've noticed, since at least 2012 on the Maiden England tour, when Bruce "cut up" the "oh oh oh" part of Seventh Son instead of keeping it all one long note. But that's also a choice he's making so he can reserve his power for where it counts and still sound good.
The big question mark for the Future Past tour is not and has never been Bruce. He's good to go. It's Nicko. Two years off of touring from the first half of the LotB tour, and there's a marked decrease in energy and speed in many of the songs. I really want to believe it's because they went on tour and weren't 100% physically prepared/in shape and they'll be fine on Future Past...but I suppose we'll see.