Yes, I agree that it's beneficial but I'm not aware of it being "required" as a skill.
I just checked the PADI Instructor Manual again; there is nothing requiring the eyes to be open in the pool/confined water or open water portion of the OW class. In fact, the word "eyes" does not even appear in the IM. In addition, the word "eyes" only appears 5 times in 21+ years of the Training Bulletin....and never in the context of the student keeping them open during a class, but more like "watchful eyes" of the instructor.
So, while being able to open your eyes with your mask off might be useful (I do it in salt water and in pools), it is not a standard.