While playing a 3DS game, did you think there was some sort of missed opportunity? For Me (Final Fantasy X spoiler incoming):
Kingdom Hearts: Dream Drop Distance - Being that the game has this whole dream theme (where the worlds are "dreaming"), I thought it would be a perfect time to introduce a Final Fantasy world, Zanarkand (the "sleeping" version summoned up by Yu Yevon in FFX).
Since KH has never been canon to any of the FF games, they could have messed around a bit, and included Tidas, Auron, & Jecht together (three characters known to have been in Zanarkand in FFX). By clearing out the Dream Eaters & finding the world's sleeping keyhole, it would reveal that Sora/Riku, while not fully waking the world, have set it up to be awakened, and that would have to wait "for another story" (a slight nod to FFX's story).
Of course, they already have alternate versions of Tidus, Auron, Yuna, Rikku, and Wakka in KH, but if you've played DDD, you'd be well aware that the sleeping worlds play by their own rules (two different versions of Mickey are present within the sleeping worlds, in addition to the real one). Also, this would have been the perfect excuse to have Seymour as a hidden optional boss (seeing as how KH isn't canon to any FF anyways).
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Currently Playing: Hitman GO
Recently Beat: Castle of Illussion: Starring Mickey Mouse, Lara Croft GO, Front Mission Evolved