Was xz/lzma a core technology when it was created? Is my tiny "constant time equality" Rust crate a core technology? Even though it's used by the BLAKE3 crate? By the way, is the BLAKE3 crate a core technology? Will it ever become a core technology?
With free software in general, things do not start a "core technology"; they become a "core technology" over time due to usage. At which point would a maintainer have to get a TS clearance? Would the equivalent of a TS clearance from my Latin America country be acceptable? And how would I obtain it? Is it even available to people outside the military and government (legit question, I never looked)?
If that's the case, you do you. Do you also think that all other countries should do the same, and rewrite everything from scratch for their government use (without foreign, for example American, influence)? And what about companies? Should they be forced to switch to their government's "safe" software, or can they keep using Linux and ssh? What about multi-national companies? And what even counts as a "core" software?
So yeah, I don't think it's a good idea.
Corps? Aside from Intel most of them barely pay to upstream their drivers.
The govt? The US federal government cut so much of it's support since the 70s and 80s.
Maintainers need to be more stringent and vigilant of the code they ship, and core projects that many other projects depend upon should receive better support, financial and otherwise, from users, open source funds and companies alike. This is a fragile ecosystem that this person managed to exploit, and they likely weren't the only one.
And you're free to not accept amateur contributions to the OS projects you maintain. Hell, you can require security clearance for your contributors right now, if you want.
If this backdoor turns out to be linked to the US, what would your proposal even solve?