@Managed abstract internal view not allowed

According to Cédric in this this post on the dev mailing list, it should be possible to have a managed internal view of a binary spec that is an abstract class, not just an interface. However, when I tried this with Gradle 2.11, I got the error:

* What went wrong:
A problem occurred configuring root project 'junit5347301453175566604'.
> Exception thrown while executing model rule: AsciidoctorPlugin.Rules#registerHtmlBinaryType
   > AsciidoctorPlugin.Rules#registerHtmlBinaryType is not a valid binary model rule method.
      > Internal view org.asciidoctor.gradle.model.HtmlBinarySpecInternal must be an interface.

I’ve posted the code to a dedicated GitHub branch bug-01. You can grab that and run ./gradlew intTest. The error appears in the test reports.

Apparently this isn’t a bug but a limitation. The example works fine if I don’t attempt to register the binary type implemented as an abstract class. Which makes me ask whether there’s any need at all to register derived binary types.