Apart from finding other things to do with my time one reason I shelved it that I was pretty unhappy with the i/o mechanism i came up with. It was just a pile of pointless boilerplate and fucking around and it wasn't fun to write and wouldn't be to maintain ...
Thus I think the first thing I want to work on is changing to an embedded database, and let that handle all the shit. Fortunately berkeley db-je has a rather awesome persistence interface and so i'll be using that. The only thing I need to manage is tracking unique instances of live objects, but that is really very little work.
At first I thought i'd have an issue with prototypical objects - i.e. loading base state from an object, which then becomes a live copy - but I can just use a separate store (aka 'database') for that.
Anyway this isn't going to be a high priority and i'll only hack on it in bits and pieces when I have the time and energy. I think the design work I did earlier will make it fairly simple, although it might need some tweaking to fit.