You are both partly right
Let’s try an analogy with Groovy.
Groovy.py is a Python implementation that supports Groovy 1.x (the language) and Groovydoctor is a Ruby implementation that supports the latest version of Groovy (still the language).
It’s the same with AsciiDoc (the language) with AsciiDoc.py (legacy Python implementation) and Asciidoctor (current/reference implementation) that supports the latest definition of the langage to date.
The AsciiDoc.py project will (soon) move out from https://asciidoc.org/. This website will become the homepage of AsciiDoc the language.
@melix If you are interested in working on a Java implementation of the AsciiDoc language, you should reach out to the AsciiDoc WG.
A first step would be to send an email on the mailing list: Mailing list: asciidoc-wg (121 subscribers) | Eclipse - The Eclipse Foundation open source community website. to tell that you are interested in contributing on the Java implementation.
You can join as an individual contributor or as a Gradle employee (if Gradle wants to join the AsciiDoc Working Group: Explore Our Members - Eclipse AsciiDoc | The Eclipse Foundation).
I know that some people working at VMware/Pivotal have also express interest in working on the Java implementation.
For reference, we will be working on a Java implementation as part of the Eclipse specification process (i.e., as an Eclipse project).
Other new or existing implementations (Rust, Go, JavaScript…) are willing to become compliant implementations and will work with the AsciiDoc WG. Please note that it’s not required to become an Eclipse project in order to be a compliant implementation. In other words, you could work on your own on another Java implementation and still be a compliant AsciiDoc implementation (if you pass the TCK).
I hope this clarify things!