So was Android.
It's a bet on Rubin himself and the team he's recruited, not on the current product.
I wouldn't support a different app store that competes with Google for control of Android.
There are substitutes for Search, Gmail, Apps Suite and Chrome, but the rest of the basic services are not that easy to replace. Maps with turn-by-turn directions, Google Translate, Google Photos with unlimited backup are all essentials for mobile consumers nowadays.
The real thing pulling to centralization is Google push, which requires play services, which requires playing by Google's rules.
If you don't have Google push on Android, you have to allow all the apps that want to get notifications from the server to keep open their own connections (which they may not have code for), which is going to kill battery life. The alternative is doing your own push services, but then you need to convince apps to support that, which generally requires apparent probable market share. Amazon managed to get some apps to do it for the Fire phone, but that didn't really go too well.