That is to say, if somehow Stadia is successful then I expect a long term outcome where games are nearly all freemium adware or grind-to-win, with a few poorly-performing notable exceptions; mashing out the same three or four proven-successful concepts with new skins ad nauseum. The margins will be so razor-thin that there won't be any room to risk on innovation.
This is because they don't care to improve discovery on their store front. It's always been awful, it will continue to be awful. There will be virtually no quality control to speak of, with sudden and opaque decisions to remove products, and so on...
Recall that in the very early days of the Android app store it was flush with $20 games, and effectively absent of stolen content, adware and spyware. Look at it now.
The two major improvements that it might have over the App Store experience would be an absence of asset-ripped "clones" (read: your APK is ripped, minorly re-branded, and re-uploaded with a similar name), and perhaps far less malicious software, because access to the local device will be limited.