git-annex is, IMHO, by far the best solution.

Pros of git-annex:

- it is conceptually very simple: use symlinks instead of ad-hoc pointer files, virtual files system, etc. to represent symbolic pointer that point to the actual blob file;

- you can add support for any backend storage you want. As long as it support basic CRUD operations, git-annex can have it as a remote;

- you can quickly clone a huge repo by just cloning the metadata of the repo (--no-content in git-annex) and just download the necessary files on-demand;

And many other things that no other attempt even consider having, like client-side encryption, location tracking, etc.