Alright, here's the main "leaks"/rumors I know of:
Doujin leak-Alleges Reimu is coming to Smash. If I remember correctly, she was supposed to kick off the pass, but got delayed due to COVID. Also, ZUN is trying to push the series. I don't quite remember the details or if it's deconfirmed or whatnot, it's mostly just been lurking around in the shadows so far.
LoL rep-Claimed there would be a League of Legends character, a Hollow Knight PreMiium, and Trials of Mana Spirits. The latter came true, no word on the other two just yet.
Ness glitch-Apparently there's a glitch involving Ness, and that usually signals a character based on someone else. I know Neku was suggested, and I think Reimu was suggested once based on proportions...? I dunno, this could potentially lead anywhere.
CacoMallow-Probably dead, or at least on it's last legs. Assuming it was playtested around Terry's release, Cacodemon and Mallow would be released around the Byleth-Min Min timeframe. It didn't come with Byleth, despite the sizeable amount of Miis that released alongside them, and Min Min got nothing regarding them either, though we did get a Bethesda costume in Vault Boy. Probably fake, if we get nothing for FP7 it's done for.
Anything I missed?