They might have some way to make them appear in this game, yes.. but considering that D2-D4 story might not have happened yet, their appearance might be a little bit..strange. Looking at D2-D4 cameos, eventhough they're cameo characters we can still see a little bit of development that makes them follow a certain timeline. For example we could see Zetta actually has his body again in D4 while he still in the form of book in D3. Most prominent example might perhaps be Flonne in angel form and how she appears to recognize Raspberyl in D4..
but since this one happened right after D1, we might not see those cameo characters and how they develop from their original story
It's not a big deal though since their 'development' have never been that much to begin with... but it really kills the possibility of seeing a cameo character with more development than their original counterpart.
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http://www.siliconera.com/2012/10/23...-a-new-series/
more news... holy crap, stop taking my money NIS ._.