In addition to making the request difficult for systems like git, if inconvenienced storage formats are exempt then this could easily be a loophole to circumven

In addition to making the request difficult for systems like git, if inconvenienced storage formats are exempt then this could easily be a loophole to circumvent the GDPR entirely. Facefriend, Instatwit, etc could, e.g., store all user data in something like git (your messages are committed using your name, etc) and point to this convoluted system as an excuse to not comply.