If someone were able to compromise the developer account and get a malicious version distributed through the Chrome browser gallery, that would be a huge problem. The kind of thing that has been making headlines with compromised npm modules recently.
Google has reviews in place to prevent malicious extensions from being distributed, but they can't be perfect. We've seen that repeatedly with both Chrome extensions and Android apps.
Every extension with permissions set for "This can read and change site data on all sites" has a huge target on it, and the fewer things using that level of access the better. Ad blocking extensions are an obvious place to look for improvement because they're so popular.
I hope that Google can put a blocking system together that will be able to perform as well as existing solutions without adding any huge security risks, but I also agree that it's problematic that their incentives are to do the exact opposite.
It'd make the Content Blocker API kind of pointless but that'd be safer than letting third parties in.
I'm so tired of this trend where folk keep pitching significant reductions of technical capability as some kind of "win" for the consumers and developers of a platform.
This is about exploiting platform owner privilege, no more and no less.
Current ublock origin.
Your adblocker frequently updates lists of patterns to block via any of many user configurable lists.
When you load a site ON YOUR COMPUTER it consults all those lists including custom ones you create yourself for annoying elements on particular sites before loading content. It NEVER sends said content to the adblocker or leaks your information.
Ublock origin provides both the adblocking engine and the lists and can innovate on the former and iterate on the latter as fast as you please.
New chrome restrictions.
Google provides an adblocking engine substantially inferior to ublock. Extensions are able to provide only a list much smaller than current lists and can only update that list when the extension itself is updated. They cannot innovate on the adblocking engine as they are stuck with the crummy one an ad company provides. This basically ensures that ad providers win the arms race with adblockers.
Safari
Shares the same inherent flaw with chrome that Apple will be providing the adblocking engine with the possible benefit that apple isn't directly making money off ads and has less incentive to directly break adblocking.