First of all when discussing about offline edits we should make effort to draw attention that "offline" could mean different thing to different people.
Offline editor from the point of view of the app's software developer might mean that editor can sometimes survive few minutes of lost connectivity, after which it will reconnect and possibly sync the team work.
Offline from the perspective of a team of scientists writing a joint paper means that some of them will take their work truly offline, to a secluded mountain hut, for an extended period (week or month) and will come back with a complete rewrite of the text to the point of being unrecognizable to the other authors. And then the coauthors will disagree with most of it, and will want to revert some of the pieces and keep some other pieces.
And scientists are not the only people needing joint collaborative environment. And not just for short papers. Few years ago, I was working in a larger team with a group of people doing revisions of a book, and there were so many revisions and revisions of revisions of revisions, and zillions of comments, that we had to split the book not in chapters, since Word got stuck even with 20-page chapters. We had to split the chapters in sub-chapters, of 5-10 pages in separate files, so that the processor would not get stuck with the myriad of comments and revisions.
These are all separate scenarios in collaborative writing, and there could be many other scenarios, so any solution should first explain for what type of scenario is it really targeting. Automated sync of collaborative work is not always the best thing to do.