If the rumors are true that YPN earnings will go down drastically when YPN is released to other countries, then most of present beta testers would have no choice but to go back to Adsense where the real money is.
YPN's future to rival Adsense depends on one and only one thing: eCPM.
Since Yahoo has much more diversified business, one would assume Yahoo would take a smaller junk out of everyone's click unlike Greedy Google which badly needs the advertising money for R&D to introduce new applications every couple of months.
Unless there is an unlimited supply of high dollar ad campaigns, its inevitable that the earnings will decrease. Once its open to the public, publishers with far more impressions than most will no doubt drain many of the premium campaigns that we're enjoying now.