This sounds like a pretty cool idea. I'm assuming it isn't open source, but do you plan on allowing data sync without any sort of cloud offering? E.g. either sync to a local directory, webdav/etc, or allow self-hosting a sync service.

Even with e2ee, I don't really want to store my documents somewhere I don't control. And if you're targeting businesses, some businesses won't even look at the product if they can't control the data completely.