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The only problem is that while creating Gen 6 sprites won't be all that hard, if you only go off of official Sugimori artwork and game animations that is, the time in creating them could take a while, maybe even slightly longer of you want them animated. Plus, there might even be a debate on the best looking sprites to use seeing as how they wouldn't be the official ones.
All simulators will still use Gen 5 sprites, but you wouldn't be able to use Gen 6 'mons in any simulator quickly after release, or whenever any roms hit the web, like you could with previous gens.