There are roadblocks and deficiencies though, a major one being that sideloaded app stores cannot automatically update their applications, making them permanently inferior and crippled compared to Google's offering.
Also, some apps from F-Droid are crippled compared to what they can do when downloading from Play Store, eg. the K9 mail app from F-Droid doesn't have support for push email, it can only check at intervals.
I don't know what the reason for this is, but the result is that Android is not a truly "open" platform.
