No need to speculate: as mentioned on the Add-on ad page: “Add-ons are currently in the developer’s preview. Although the functions needed to create add-ons are available to everyone, only approved developers can publish the store. Please apply when your add-on is ready to launch. "
The value on which only approved developers have access now ... The applications that are now available were developed in the period prior to the release of TC and by selected users.
Perhaps someone from the Google development team will abandon ETA, personally I don’t know ...
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