The CPA ads aren't part of the Adsense content network and aren't contextual ads (yet). The publishers would need to opt into the new "referral" program and pick and choose which advertisers to promote, so the Adsense PPC model is alive and well - so far.
If the pricing is attractive it's possible that that a bunch of advertisers will abandon the Adsense content network in favor of the new CPA option. Or maybe the ones to be hurting will be the big affiliate networks like CJ.
Only 1 thing is certain: Google does something new and somebody, somewhere will feel the effect!