Who's we? Americans? Sure that's fine for you, but Americans aren't exactly trustworthy outside of the US either and I say that as someone who's usually pro US. This sort of mentality just shows a lack of understanding of how most of the world sees the US. Even in places like say, france, the us is seen as an ally but a very untrustworthy one. Especially since out of all the confirmed backdoors up until now, most of them were actually US made.
If this backdoor turns out to be linked to the US, what would your proposal even solve?
"We" doesn't have to be the U.S. This is a false dichotomy that I see people in this thread keep pushing. I suspect in bad faith, by the people that want to insert backdoors. As a baseline, we could keep the contributors to NATO and friends. If a programmer is caught backdooring, they can be charged and extradited to and from whatever country.
If it's just an extradition issue, the US has extradition treaties with 116 countries. You'd still have to 1) ensure that user is who they say they are (an ID?) and 2) they are reliable and 3) no one has compromised their accounts.
1) and 3) (and, to an extent, 2) )are routinely done, to some degree, by your average security-conscious employer. Your employer knows who you are and probably put some thought on how to avoid your accounts getting hacked.
But what is reliability? Could be anything from "this dude has no outstanding warrants" to "this dude has been extensively investigated by a law enforcement agency with enough resources to dig into their life, finances, friends and family, habits, and so on".
I might be willing to go through these hoops for an actual, "real world" job, but submitting myself to months of investigation just to be able to commit into a Github repository seems excessive.
Also, people change, and you should be able to keep track of everyone all the time, in case someone gets blackmailed or otherwise persuaded to do bad things. And what happens if you find out someone is a double agent? Rolling back years of commits can be incredibly hard.
Getting a TS equivalent is exactly what helps minimize them chances that someone is compromised. Ideally, such an investigation would be transferable between jobs/projects, like normal TS clearance is. If someone is caught, yes rolling back years isn't practical, but we probably ought to look very closely at what they've done, like is probably being done with xz.
If the ultimate goal is to avoid backdoors in critical infrastructures (think government systems, financial sector, transportation,...) you could force those organizations to use forks managed by an entity like CISA, NIST or whatever.
If the ultimate goal is to avoid backdoors in random systems (i.e. for "opportunistic attacks"), you have to keep in mind random people and non-critical companies can and will install unknown OSS projects as well as unknown proprietary stuff, known but unmaintained proprietary stuff (think Windows XP), self-maintained code, and so on. Enforcing TS clearances on OSS projects would not significantly mitigate that risk, IMHO.
Not to mention that, as we now know, allies spy and backdoor allies (or at least they try)... so an international alliance doesn't mean intelligence agencies won't try to backdoor systems owned by other countries, even if they are "allies".
The core systems of Linux should be secured, regardless of who is using it. We don't need every single open source project to be secured. It's not okay to me that SSH is potentially vulnerable, just because it's my personal machine. As for allies spying on each other, that certainly happens, but is a lot harder to do without significant consequences. It will be even harder if we make sure that every commit is tied to a real person that can face real consequences.
If this backdoor turns out to be linked to the US, what would your proposal even solve?