title: ServiceStack DTO with inheritance
body: <p>According to Mythz (<a href="https://stackoverflow.com/questions/10750571/getting-servicestack-to-retain-type-information/10759250#10759250">Getting ServiceStack to retain type information</a>) he recommends not using inheritance in DTOs. What about the use case where I want every request to optionally provide an API key, or a location parameter? Are interfaces bad to use but abstract classes are ok? Anyone have any recommendation?</p>