I'm as sure as anyone can be who doesn't work for Yahoo! that they will offer something comparable to link units at some point. They're going to do everything they can to take publishers away from Google, and that will mean mimicking the various ad types that AdSense offers.
I've been testing YPN thoroughly with close tracking, and my advice is to closely analyze your pages running AdSense now to find those that are performing poorly. Move all the pages that get low CTR and low EPC to YPN. Seriously, EVERY page on my sites that I've followed that pattern with are doing a LOT better with YPN. That's several hundred pages across many different industries. It's 100% foolproof (at least so far).