So excited about this, you have no idea.
I use a Microsoft Surface Pro 3 because I needed to be able to capture "digital" handwritten notes in a way I could make use of them on multiple platforms (Mac, iOS, Windows) and have access via the cloud. While there are some great note apps for the iPad (Noteshelf is my favorite), none have had good cross-platform two-way sync with cloud storage systems. A couple offer Evernote upload, but it's not quite what I'm after.
OneNote on Windows, Surface and Android allow editing of text, ink notes, OCR, etc. The iOS versions could always display the handwritten notes though I couldn't use a stylus to add additional text or diagrams.
Very pleased to hear it's been added to the iPad version. Not critical on the iPhone given the smaller screen size (even my iPhone 6 Plus is too small to really bother with writing on the screen).
OneNote is a great app and so happy it's getting good attention from Microsoft.