Minor Description
The org.apache.sis.metadata package contains a package-private PropertyDescriptor class, which currently implements org.opengis.parameter.ParameterDescriptor. The later is not really appropriate since metadata are not parameters. A better choice would be ExtendedElementInformation from org.opengis.metadata.
In theory, ExtendedElementInformation is only for extension to the ISO 19115 standard. However, its API appears to be also suitable as a reflection API for ISO 19115 itself.
While the package-private class is not directly exposed to users, the interface implemented by this class is accessible by users. So the choice of ParameterDescriptor / ExtendedElementInformation is significant.