Its uncertain whether there will be another PR Update at all. It made it a bit too easy to find good domains for pbns I think. Everyone who says to concentrate on PA / DA is an Idiot because it can be faked easily. Yes, it was easy to fake PR as well but it gave you an indicatioin where to start looking and analyse backlinks. Now you have a much larger pool of domains you have to throughly analyse to find the good domains. Also, if you want some metrics that are a lot harder to fake than PA / DA and, imo, say more as well, look at Trust and Citation Flow. CF is easily gamed but TF just isn't.