I also agree about Ads should be a built-in function, not as plugin.
Because when we use Ads extension from CocoonJS we can't control Ads placement for each layout specifically, using CocoonJS Ads will be showed from begin to end using same type of ads and same placement and that will give bad experience to players and lower revenue for developers.
If we can control Ads placement at each layout we can provide better user experience such as we can place full page Ads before game start and game exit, banner ads for menu/level selection and in-game layout without ads so player can playing game without distubed by ads and with this ads placement setting also will improve developers income from Ads.