Google should provision for other Android stores in its ecosystem.
While Google probably enjoys its monopoly shop on the standard Android system, they might make more profit in opening the system to other, reputable, app stores as equal partners. It could be a massive selling point: "You could visit the apple AppStore, or you could visit the Android AppMall."
I seriously doubt that Amazon wants to sell tablet hardware at cost or at a loss. What it does want is a storefront on tablets where it doesn't have to pay the Apple 30% cut. Instead of being a competitor, Amazon could add its huge content library to the stock Android experience-- oh, and they'd probably become a huge asset for selling Android tablets (that don't compete with normal Android).
Valve is developing Steam for Ubuntu, This is, at least partially, a reaction to Microsoft locking them out of the Windows RT ecosystem. They've already got an Android app for the Steam contact list; I bet they would like more. Getting an Android Steam Store could be a massive boost for Android as a gaming platform.
Other potentials for top-tier Android stores could be Barnes and Noble, or EA's Origin (I'm no fan of Origin, but it's a possibility).
Another long-term effect is that it could bring legal trouble to its competitors. Right now, these monopoly-in-their-ecosystem stores survive because, hey, that's the way it's done. Thing is, as soon as one non-monopoly manifests, that could create legal pressure on the other big ecosystems to open their stores up as well.