Is your feature request related to a problem? Please describe.
When using a pack like xali's enhanced vanilla with Iris and a shader you can clearly see issues with connected textures due to them using the wrong material.

Describe the solution you'd like
I'd like support for this to be implemented. I know it must be possible because it is working correctly in Optifine

Describe alternatives you've considered
There's no alternative other than disabling connected textures or moving to Optifine

Additional context
It looks really bad on Complementary's upcoming colored lighting update.