Implement a default strategy that includes selected mgnl properties (tags mostly); this strategy should be swappable by configuration.
Other policies could be implemented to white-list specific properties, or include more jcr/mgnl-prefixed ones.
- keeping mgnl: props but not jcr: ones
- specifying mgnl sys props to include by mixins
- what to do for other domain-ish content (mgnl:template or mgnl:type for blocks)
- give flexibility via query-params?
we could/would probably complement that with separate @nodeTypes and @id special properties.