There's no way they'd know beyond maybe a second fighter's pass, but even then, they'd just be ideas at that point. Negotiations wouldn't start for a while as is, as that's way too much pressure to work with when they have 6 characters to currently work on with a smaller team.
A lot of these leaks are very unrealistic, and it's not because of the character choices. Anything past the first Season's Pass is unlikely to remotely have anything beyond maybe some talk. And that's it. A leak actually announcing a second one is coming would still be more realistic. The only leaks I feel have a tiny chance of being real will only have content from the first Season's Pass(and other small snippets like other Mii Costumes, individual packs or characters or stages that are not Season's Pass-related. Like, Echoes could be a separated thing. Same with stages. They sound realistic enough since even with Echoes, they don't take long to make).