Of course, it does depend how reasonable a company and/or their associated creators are. For instance, Nintendo and Sak had to give an arm and a leg just to get songs for Dragon Quest from Enix, and even then they weren't orchestrated, let alone remixed in any form.
While it's hard to tell if Square-Enix will let any of their other related characters in here this time, getting Crash doesn't seem overly complicated; he's fully owned by Activision to the point that every character in the franchise can be used by them, no matter who created each one in the first place.
In any case, it's quite clear that as far as Smash inclusion goes, there is no question that
took priority due to their historical fan demand. Even if Chief and/or Steve can't get in this time, the door will always remain open since Microsoft has firmly stepped its foot into Smash.