OK, pretty good, can we add a subclass to dialects/postgresql/psycopg2 that makes use of psycopg2's built in JSON processing?  this is what the HSTORE type does, there's some relevant lines at:

https://github.com/zzzeek/sqlalchemy/blob/master/lib/sqlalchemy/dialects/postgresql/psycopg2.py#L157

https://github.com/zzzeek/sqlalchemy/blob/master/lib/sqlalchemy/dialects/postgresql/psycopg2.py#L233

https://github.com/zzzeek/sqlalchemy/blob/master/lib/sqlalchemy/dialects/postgresql/psycopg2.py#L414