since conversion rates are not static, advertisers usually have to build some padding into their maximum bids - this padding ensures that they maintain a positive ROI.
this new CPA-target bidding could serve to reduce this extra padding out of advertiser bids.
of course the opposite could happen as well, as advertisers that were overbidding could lower their bids to the ideal spot. i think it is safe to assume however, that there are more underbidders than there are overbidders.
i wouldn't be surprised if this new system results in some small increase (perhaps imperceptibly small to the average publisher) in bids over time.
