Great to see your recent work on the language.  Very clean.  You said it would change so here goes..

It would be very cool to get rid of this: `Balance.save(to)` and this `Balance.save(from)`.  The contract would need to be transactional to some extent so a failed assertion or error would roll all the changes.

This is motivating me to add your text format in a struct serialization parser.   Using text in addition to json is a very easy enhancement.