I believe there are nuances in interpreting questions like these. Maybe this was meant to highlight what differentiates OP's business compared to Evernote. Just because someone couldn't do it, doesn't mean it's impossible. Everything successfully done might have had enough numbers of failures before someone showed how it's done.
It's not meant to be harsh, rather just realistic, productivity apps are a dime a dozen (there's literally hundreds of submissions like this over the years on HN). OP needs to know what makes their submission different.
If I'm not mistaken Evernote had tens of millions of users.
I'd assume a note-taking app with a better UX has the potential to have at least the same ballpark. I think Evernote's mistake was raising too much money and not differentiating the product from competition...
That said, I really have no idea about conversion and monetization of such an app, because I couldn't find anything comparable.
Compared to Evernote, Remindful doesn't require you to manage your notes, can store complete documents and articles and answer questions about any part of the content.
Moreover, it would be able to actually remind you about important dates and things.
So far people I've spoken to said they need something like this, but at the moment the MVP is not quite ready to be able to charge for it...