For developing systems that integrate with Aha.
It would be really useful to query the Rest services for a particular Aha object to determine what fields are required to create or update that object. That way validation can be performed programmatically on any payload going to aha and reduce potential errors that Aha would have to handle.
Also it could have some descriptions of all the available fields with any explicit values so that the whole payload can be validated.
Metadata retrieval is definitely needed in the Aha! API.