I've actually just recently launched an app for iOS on the app store. It does outlining similar to how WorkFlowy or TaskPaper do it, and in the next update (awaiting approval as we speak, ETA 1 week) it has full Evernote integration, letting you attach Evernote notes anywhere in your outline.
In the future I plan on adding a feature to export an entire outline (starting at any "node") to Evernote.
And here's a screenshot of what the Evernote integration will look like:
I hope this isn't considered spam, as I think it's very relavant to this conversation. If it is, I can remove it, or if it would make a difference, post a bunch of promo codes so people can try the app for free.