people tend to underestimate chances of Crash being on the base roster. Sure, I also agree that he would be a good fit for DLC since he'd actually sell by himself a whole lot, but there's also the risk of Smash Switch lacking that heavy hitter 3rd Party guest for the base game.. (Rayman? Bomberman? great choices, but not that gigantic icon that Crash is, or how Snake, Sonic or Pac-Man were in the last two entries). Unless they want to sell the game with no cuts from Smash4 (which is something I personally believe), and call it a day until DLC comes.
Again, Nintendo and Activision were close together by the time Crash revival was on works, it's a safe assumption that they were at least aware of future plans. --Nintendo wouldn't allow their characters in Skylanders having a crossover with Crash Bandicoot if wasn't for that. The very announcement of N. Sane Trilogy for Switch means little on the big scheme of things.. of course it helps (it's a game that it's a mutual interest for both companies to promote once the character is added in Smash), but there's way much more to take into consideration.. that's not the solely reason that Crash would be added.
Western characters is always a big mystery for Smash Bros. and being popular in Japan is a trump that few of them have, and Crash has that in abundance. So, at least is more believable they'd incline to pick a character that have some significance for Japanese players.