This is amazing work! Just tested it with the latest dev build and it works.
The only issue I have is the non-support for animation player. It completely broke my cutscene system as I can no longer add animation on the timeline using the Spine animation track.
The only way around this issue I can think of is to write functions that plays the animations I want and then call the function in the timeline but this looks very cumbersome.
Is there a way you recommend for making cutscenes in the timeline using the new Gdextension?