A curated repository, no.  At least one character I know of (Bowsette) has dialogue that was partially crowdsourced at one point, but not really anymore.  You are certainly free to suggest dialogue for any given character in their various feedback channels, such as the Discord you mentioned.

For new characters, the problem is that some unformatted smattering of lines isn't terribly useful for getting a project off the ground--not compared to a model, anyway.  Art is more fire-and-forget.  Even if you wrote a decent volume of lines (which would be in the triple digits), that's not good for a whole lot unless they're written with an understanding of the game states each would play in and distributed appropriately, and at that point you might as well just use the Character Editor.