Feet used to going bare don't need to look any different to any other feet. The skin thickens but it doesn't just build up dead skin and harden. The only callouses you'll ever see are relics from blisters which will tear off eventually, and they're not essential to keep your feet in one piece. You never lose the sensitivity - you can always feel everything. it's just that it's not uncomfortable because you get used to it, and you know that your feet aren't harmed and that your feet can handle it, so the feelings aren't painful, they're just there.