They proposed an API that was like safari where the block lists are handled by a pattern match inside the browser rather then running a js script.

They made this announcement increasing the number of patterns that can be matched however the API remains the same.

Now it could be that google is trying to undermine add blockers in order cement its power. However this argues agaist it. Since the list is limited and google is the largest provider of adds if there are insufficent patterns then blocking google ads would result in googles rivels not being blocked.