Adding support for collision detection to nix, involves a one or two line change to libstore. You should implement such an assert statementt and contribute it to Nix. Nix is open-source and would likely gladly accept it.

You are way overstating the importance of this. This is not a fundamental design flaw in the nix ecosystem. If there's actually no check it's because most people realize this is not a problem worth spending a lot of time on. But the time required here is a few minutes at most.