Solution should be a generic CRDT implementation with concepts of change log with unique identifiers for each participant and operation. But we also need a filesystem/operating system support for merging. As otherwise you will need to have a unique file for every operation to cope with merging. Or you have app specific merging and no data interoperability between apps.

My "small" wish would be to have a local but replicated data format for a text file. So I can edit it in any editor while still retain the history and allow for collaboration from multiple devices. I'd love for it to be shared between devices using dropbox and iCloud depending of the user.