I'll tell you right now, the size of your wrists/ankles has about as much to do with your powerlifting potential as the length of your fingers or feet. Sure, there is *some* kind of effect, but having a less than neanderthal bone-structure wont keep a dedicated, intelligent, driven and skilled lifter out of the record books. Yes, Ed Coan had a distinct advantage from the start, but had he not the same drive or attitude we would have never heard of him.
I never had a terribly thick bone-structure, but I've done okay. If I had more patience for using gear than I do, more money to buy gear and perhaps a little er, 'ergogenic aid' I would be making a run for the IPF record books right now.
Besides, if you train seriously, and seriously hard for a few years, by that I mean years and years of heavy squats and deadlifts, you will most certainly increase your own bone density. It's not just muscle you build when you jump 3 or more weight classes in years of training and competing, it's your whole structure. I have gained over 50lbs of solid LBM in years of training hard, but I can guarantee you that if I stopped training tomorrow and never lifted a weight again I would never ever be as light or as small as I was before I found powerlifting. You cannot build wrist size up with exercise, yet, my wrists are measurably thicker than they were 5 years ago.