Ambient sounds are definitely planned, it's not intended to be dead silent forever there.
And the footsteps do vary by three different surface types at the moment. No plans to add in further anytime soon, although Pablo did do sounds for two more kinds. But the coding on that is really tricky for now, because answering "what kind of surface am I standing on" is surprisingly difficult. Not impossible, it's just not set up to efficiently answer this question.