Right now, the storage system is scattered. It provides 3 builtin storage systems, plus the JSON being used for the OAuth token.
I'd like to suggest unification of all the storage systems into a single JSON-backed system (since it's the smallest files and the world seems to have settled on JSON).
Upgrading is the hardest part, but this could be done transparently by having the Read method automatically fall back on the old system and upgrade them to JSON before returning. We could obviously leave $format in, deprecated.
Or we could just add JSON as a fourth format and convert most of Contra to use it. Discussion is required.
If we want to do this, I'll write a patch, add code to this issue, and upgrade to a pull request.