Ideally this would be using the same format as the save command (.mat file), but instead of writing to disk directly, it would write it to data in memory. The reason is I need to access the saved data directly to implement a custom hashing method on the variable, and have no need to write it to disk in order to achieve this, and would rather not go through the administratively-heavy option of creating a ram disk through ramfs.
I'd actually be OK with a version-change of MATLAB invalidating the object in my particular case (the idea being that any software updates may influence results, however unlikely).
Assuming full .mat support is not an option, I still need fairly general support, which is why the (intermediate) output of save seems like a good option: e.g., nested structs, cells, arrays. I could probably do without Java objects in this particular case.