It all depends on what the certification process looks like and how much it costs. If this certification process is particularly technical or costly it will force out smaller publishers. This is good or bad depending on your perspective.
Increasing the barrier to entry means that only those with the finances already in place and the ability to execute a technical audit will be able to access these larger, and likely higher eCPM, advertisers. For those publishers it would increase the ad quality, ad revenue, and lower malware, etc. Publishers will also need tools to fight bad or low quality traffic on their end. If the tools come to market it’s a win-win-win for those with the resources.
Unfortunately it’s probably bad for those publishers just starting out. They’ll have to contend with lower eCPMs, more malware, and an overall worse experience for their users. This makes gaining traction more difficult for them.