If by "Git for data" you mean accumulate-only (or append-only), immutable data stores... There are already many existing solutions. It's always good to see alternatives, though!
* Convert the versioned data to tab-separated values
* COPY it into Postgres every time
* Hope Postgres can act immutable enough even though it wasn't designed to be
The closest I've come to improving this situation was Kyoto Cabinet (unusable license) and rolling my own damn hashtable (it worked okay but adding new kinds of indexes was just unmaintainable, there's a reason databases should be made by experts).
Pachyderm is git for data. We work hard to make sure we can store data of different types (binary, text, json) efficiently. We also work hard to give you good mechanisms to read the data in a distributed way. I'd be curious how this suits your purposes.
While I can see how a git-based filesystem can help with some use cases, does it do any kind of indexing at all? I see that the FAQ recommends exporting the data from Pachyderm into PostgreSQL, which leaves me where I am now.
The nice thing about git is that it doesn't really require much of the server. I run my own "git hosting" with linode, apt-get, and ssh.
Most of the solutions for immutable big data don't have that level of convenience, as far as I know. Anything which requires a lot of sysadmin and ops work will eventually become a commercial cloud service... git on the other hand is useful by itself, and good companies can obviously be built on top of it as well.
The difference between this and a version control system is a major part of why the UI is so awful.