There is also no way to verify that the software that is being installed is not going to do anything bad. If you trust the software then why not trust the installation scripts by the same authors? What would a third party location bring to improve security?
And generally what you are describing is a software repo, you know the one that comes with your distro.
5 years is optimistic. More likely 10-20 years at least. Established languages have a lot of inertia and it takes a very long time for that to change.