anyone know if all of the bending and stretching in yoga can be problematic to your foot/ankle in terms of the biomechanics of all of its weight-bearing poses?
No. My feet are just fine after years of pilates and yoga. 👍 My back is another story.
If you practice yoga properly (i.e. don't go to a studio that is hopping on the yoga bandwagon) I don't see why it would harm the feet. Don't push your body past what it can do. Yoga should help you achieve balance and alignment from your toes through your skull so it should improve biomechanical problems due to poor posture (perhaps abnormal gait as well).