For what it's worth as someone involved in GNOME, I don't see how an *official* GNOME "application store" could work without a sustainable business model for humans to review code in order to ensure we're not shipping malware.
What we can enable though is third parties to distribute applications, whether Free Software or not. Not of course that this hasn't been attempted before...the internet is littered with various ones like Autopackage and such. It's not an easy domain.
However, I think these previous attempts were addressing an actual need, and could be made higher quality if they were integrated into the core of the system rather than an add-on.