I think there's now a blurred line between todo app and knowledge management, especially as tools like notion (and for that matter Dendron), are making it more viable to manage todos within your knowledge base.

As for YC, I remember seeing at least two other note taking companies within our winter batch. At AWS, the mentality for new services is to "let 1000 flowers bloom" (and see which one's make it). Something similar is happening in the note taking space right now