There's this:
Otherwise, nothing like that comes to mind; I think the only times that we've gotten three or more reveals were Ken/Incineroar/Piranha Plant (three characters, but one was an echo fighter), the E3 where Ryu was revealed (three characters, but two were veterans and clones), and the direct that revealed K. Rool and Simon (five characters, but three were echo fighters), and every single one of those were Smash-specific presentations.
I figure we're going to get a Direct in the next week or so (otherwise, we know absolutely nothing about the rest of Nintendo's 2020 line-up), but three new unique characters in one Direct seems implausible. I could see two getting revealed if we do get a Direct, since I'd assume that the reveals would have been intended for E3, but three seems like a bit too much, especially if it's a general Direct as opposed to a Smash-specific one.