I'm curious if Sephy will get a new stage, though, considering that we already have Midgar and Midgar is all that the remake has done so far. Knowing Nintendo, the extent of their creativity is that they'll just have another Midgar stage based on the Remake with maybe some floating platforms that move every once in a while.
Someone didn’t watch the trailer, a massive love letter to Advent Children which is weird because Sephiroth is barely in it. Sorry, spoilers for a 15 year old movie. I digress. Every DLC character gets a new stage. 1:30 in the trailer shows the new stage for the first time. Looks like the Northern Cave with Lifestream making an appearance. Sorry, spoilers for a 23 year old game.
Yes, that's why I came back and removed that text. I rewatched the trailer and saw that.
Incidentally, as little as Sephy's in that PoS Advent Children, at least it was longer than he was actually in the original game.

4/4 so far on disappointing new character announcements in this 2nd Fighter's Pass. I mean, we could have at least gotten a character from a DIFFERENT Final Fantasy game than the one we already had.
Let’s not kid ourselves here. You would’ve been disappointed regardless because you’re always disappointed. Have you considered not buying the DLC?
Sure, I'll likely always be a little disappointed to some extent since the characters I'd like to see in Smash are a little more obscure (which, IMO, is what this DLC should be for, since you're catering to the hardcore, but I digress). Still, compared to the 1st Fighter's Pass, the 2nd's felt pretty lacking so far. Hopefully the last 3 characters pick up the slack. I could have sworn we were on character 4, but we're only at 3.
As for "not buying the DLC", it's Smash. Nintendo's not putting out SP content for it and we won't be getting a new Smash for at least another generation, so you either get the new characters & stages, or you don't play the game.