Have not started on 4.0 yet, but will be looking into it after the holidays. Glad it's working for you at the 3.8 level.
Originally, I was going to wait for C3 webGPU support to do 4.0, but after discussing with Ashley, at least the first version of C3 webGPU support will limit how we can do Spine tint color, tint dark color. So, now I will focus on 4.0 after the holidays with the current WebGL support.