An interesting idea, but I would guess that it is far to complex to try to integrate OneNote or another application, like Evernote, inside of TB.
I'd be happy if we just had an easier way to link Evernote notes, OneNote notes, et al. to thoughts in TB, than the current right click to get a hyperlink, click to copy, move to TB, right click and click to paste in as link in TB; some sort of Share function, as exists for many apps in iOS. Currently, after setting up a bookmarklet in Safari, it is possible to save to TB Inbox, then drag links from there to other thoughts or new thoughts in TB. But, Safari is the iOS app I probably use the least, except when forced to use to share some item. Lots of other apps have share functions within them, but none other than Safari have a Brain function.
One of the early PIMs, Ecco Pro, back in 1993, had a feature called The Shooter, that made it quick and easy to copy and paste information between Ecco and other running apps on the PC. I don't know why someone hasn't created such a feature for modern day PC apps. BTW, Ecco Pro is still available, at http://www.compusol.org/ecco.html -- I am running it right now on the latest Windows 10 Anniversary update.