Google has always been able to do that. Just alter and re-sign the APK with their own key(s), since Google's keys are trusted by Google Play Services (third party app stores also trust Google's signing keys for compatibility reasons).
The way the Play Store is currently designed, end users don't even have the ability to view the key-path before installing a package. So detecting if it is Google Vs. app developer's signing key is extremely unlikely without copying that APK off-device and inspecting it.
All users know is: Is this using a signing key trusted by Google? Yay/Nay.
The way the Play Store is currently designed, end users don't even have the ability to view the key-path before installing a package. So detecting if it is Google Vs. app developer's signing key is extremely unlikely without copying that APK off-device and inspecting it.
All users know is: Is this using a signing key trusted by Google? Yay/Nay.