This is obviously Google trying to grab a piece of advertising budgets of apps and impact of this on "discoverability* will remain to be seen as emergent property later on. Definitely not the primary driver behind this feature.

However, before we start booing Google...

Facebook already holds unarguably the biggest part of this already, and Google heading closer to the center of that particular arena will likely result in a net positive for publishers.

My guess for would be that this will push Facebook little by little to specialize in iOS ad-mongering.