This is only an issue when someone 1. is very negligent with redistribution 2. has enough negative implications for the author to take issue with it.
NixOS is a big, funded project, what's wrong with holding them to a standard? If they package it right then moral rights wouldn't be an issue for them, it's not exactly a legal minefield.
Not everywhere has unalienable ones. You can waive them in the UK and USA, which is what publishing under a FOSS license implies, to an extent.
Anyway, moral rights aren't just about mangling a work. It's about mangling work in a way that makes the original author look bad. But with software, with the internet, no matter how bad the mangling, you can Google the author and find, say, his disgruntled Github comments stating his disapproval of the changes, so no reputational damage should accrue. Moral rights violation: nullified. Eh?