Is your feature request related to a problem? Please describe.
CEM enabled resource packs like https://www.curseforge.com/minecraft/texture-packs/fresh-animations do not work on Iris

Describe the solution you'd like
Adding CEM Support

Describe alternatives you've considered
https://www.curseforge.com/minecraft/mc-mods/custom-entity-models-cem

Iris is for shaders and shaders only, currently there are no plans for other optifine alternative features.