As of the latest documentation, there is no mention of the tint-black feature being added to the spine-godot runtime. The limitation regarding the inability to send extra vertex data to shaders in Godot still stands, which prevents the implementation of the tint-black feature. While there have been discussions and attempts by individuals, such as the one you mentioned on GitHub, there has been no official update or solution provided in the spine-godot runtime documentation.
For the most current updates, you might want to keep an eye on the Spine Runtimes repository and the Spine Runtimes Guide.
