Also, do keep in mind when Sakurai said this; this is well before there was a Pass 2 ever greenlit. It means that the only DLC was Plant, the 5 next characters, and 1-2 after. He even thought, before Pass 2, bringing everyone back is unfeasible. Now that we have 5 more characters than his maximum ideal at the time of the writing? That's even crazier.
(For some math, PP and the first Pass combined is 6 characters. He ideally had 1 or 2 more possible. Steve was likely one of them. The other is unclear. Due to how Pass 2 works, we got a total of 7 characters, as Pyra and Mythra are counted separately, instead of just named separately like Steve and Alex. Since his ideal DLC at the time was 7-8 characters. And then add 5 more for 13 total, and you can tell how crazy it gets).
It's obviously not impossible for Everyone is Here to return, but not exactly likely, and at least we have a good idea that he was already skeptical well before DLC was finished. That said, if he thought it was hard with only 8(max) DLC characters, imagine 13. People who don't think it'll happen again have good reason to believe that. Licensing, the herculean task of balancing, etc.