I think people trust too much generally. That's not going to change with any paradigm put forth. However if you're running binaries from vendors you don't trust

I think people trust too much generally. That's not going to change with any paradigm put forth. However if you're running binaries from vendors you don't trust, you're playing with fire even in a regulated app store. Most people don't change their default browser, adding third party repos would be similar. Removing the ability for the owner of a device to install software they want fixes one symptom, not the main issue of trust. Also it makes your device into a glorified feature phone. No thanks.