Is there any possibility that this course could be updated for 2.9?
Unfortunately no, it's not likely that I will be updating this course for 2.9. The value of the material is less the specifics of the software / version used and more of the conceptual workflow. Concepts can be applied to any software / version which is why we keep it published. One day if 3D animation standard workflow changes significantly we will remove it.
Blender changes too fast to re-record courses for each new version. All instructors within and outside of CGC have to deal with this curse / blessing. That's why you rarely see us re-record a course 1-for-1. However we will sometimes record a new course focused on the same material with different visual focus. So it's possible in the future we will record a new course about short film production using different characters and scenario than Piero.
aaddie78 I've created most of my Piero in Blender 2.9x and used Blender 2.66 only for the "Sculpting" and "Retopology" but I'm now familiar enough with the Blender 2.9 GUI so that it wouldn't be a problem for me to do this in Blender 2.9.
With the "Collections" introduced with Blender 2.8 you no longer need a "Scene Layer Management" addon for better organizing your mesh with layer names. There's a new addon for the "Bone Layer Management" in Blender 2.9 but it's also possible without it as I did it by simply noting in Blender's "Text Editor" the layers onto which I've put the different bones.
I've painted the feather textures in GIMP (for which I've written step by step instructions) instead of using "Photoshop" as Kent did in the course.
Furthermore, I've documentated my progress and differences between Blender 2.6 and 2.9 in the "Questions" section of each lesson. Maybe, this can be a help for you as well as the questions and comments from other people in these lessons.
Since the Piero course is a marathon and not a sprint, I highly recommend having a second shorter "Fun Project" parallel where you can reach your goal much faster so that the success there motivates you to push your Piero project further forward.