i just cant see a FF character get in that isnt sepiroth. because to the general audience, i think it will look very weird and it will raise the question to many fans "ok but why is _____ in when the biggest villain sepiroth wasn't and cloud was already in?"
i saw people on previous pages ask about how Sepiroth would fit in due to his lore. you gonna ask that same question for rosalina, palutena, shulk, bayo, or cloud? they'd just use whatever sepiroth had in ff7. and until further notice, final fantasy isnt represented in smash its literally just one game represented. That could be Nintendo decision or it could be SE either one is possible. business wise i think he is the best choice and he is the safe pick. I'd love to have kefla or tifa or even lightning. (NOT the boy band tho).
Also, if the SE character is going to be first what better way to hype everyone off but with a continuation on arguably 4's biggest announcement?