Wonder what it would be like if all the Magic Kingdom parks had Wondrous Journeys?
It wouldn't be possible for every Disney park to have the exact same fireworks/projection show for a number of reasons:
1. Every park has different fireworks restrictions, and only WDW can really do whatever they want with fireworks. DLR has stricter regulations about what they can do, when, and how when compared to WDW, and the internationals tend to be even more strict than DLR.
2. You'd also have to redo the projections for every new show. Tokyo and Magic Kingdom could ostensibly share some projections because they have the same castle, but even then you'd have to make projections for MK's Main Street, which
is a place where many gather to watch the fireworks/projection shows, that wouldn't be used Tokyo's World Bazaar, which pointedly is
not used for that purpose. With other parks, you're starting over completely from scratch because you'd have to design each set of projections differently to fit each castle. And of course you have all of the other areas that utilize projections that, even if they're the "same", are just different enough to again require them to start from scratch.
3. Different markets want/need different things from fireworks/projection shows. Tokyo's actual fireworks are super short and old school and have nothing to do with their projection shows. Because of different regulations, the focus of the show is necessarily different: in the US, the projections supplement the fireworks; in the international parks it's the opposite. Different properties attach to different properties or may have different styles. Pacing needs may be different also; Tokyo has done some projection shows that, were they to be put in the US just as they were in Japan, would probably be perceived by some as slow or boring. HEA probably wouldn't play as successfully in Shanghai because the focus of the resort (and knowledge of Disney's past films) is more blatantly on Disney, the multimedia conglomerate vs. other markets. And so on.
So you get to the point where there's really no incentive for them to share fireworks shows, which is why it's never been done. The closest you get is one fireworks show borrowing music from another, and that's probably all that it's ever going to be.