I think that when they made the Sm4sh roster, they didn't really pay attention to what the community really wanted.
It explains many decisions: The very VERY late inclusion of Mewtwo who was clearly the most wanted character, Ridley still not playable, Geno not playable, Isaac gone from the game, etc...
They just did safe bets by including characters who were popular among everyone, not specifically Smash fans, i think that's why the favorites of the Smash community were basically ignored. Remember how much Mewtwo was asked, that was insane, he was theundisputed number one in every damn poll and he was still nowhere to be found in the base game. So yeah, the less popular characters (Ridley, K Rool, Isaac, Geno) even though they were supported by many smash fans just had no chance.
Now, they pay attention to what the Smash's fans really want, we know that for a fact. There is no way that they don't know how popular Isaac is. So yeah, i'm pretty confident that he's going to make it this time !
By the way, even though i'd prefer three unique trailers, the idea of a trailer involving Skull Kid, Geno and Isaac is still awesome.