I fully agree with the conclusion that multi platform usage will be increasingly important. And not just a cloud application. I think Scrivener is vulnerable here although it's trying. Seems to be years away from an Android version. And hasn't tackled the Dropbox issues despite frequent complaints about syncing.
I use OneNote because it "works" with this functionality.
Unless smaller publishers get on board with this, I fear that Apple, Google and Microsoft will dominate even more than now. Not easy because it can't be a cheap road to follow.