methinks 500 years later, they'll show even more greenery to contrast further from the sheer vastness of the wasteland.
I mean, can't really speculate on what they'd do, but if I were directing, I'd be tempted to completely recut the ending to be a reverse of the opening.
Start by intercutting the a long zoom out of the canyon with quick shots of Nanaki and his cubs running, pulling way out until you clearly see Midgar in the distance, zoom in on Red XIII and his cubs overlooking the city, then when he roars and the birds take flight, transition to birds flying through the city over ruined a mako reactors, show scenes of wildlife overtaking the roads and skyscrapers, and perhaps close on a shot of a flower blooming on a street corner, or maybe pan up to a sunset -> starfield. Or even a foreboding shot of a black feather falling into a puddle.
Something like that, anyway.
Would also be kind of cool to maybe do something completely new, like reveal Edge 500 years in the future with humans now living at one with nature, with a completely new kind of society, architecture, fashion, etc -- something both futuristic and tribal, maybe.