Ken Thompson's speech was made two years before the first draft specification of C was published, so I don't understand how it is connected to language specifications.
Here's a way to address the issue he brings up in that speech that does not involve language specifications: https://dwheeler.com/trusting-trust/
I think the first problem is some kind of language specification. That it's not possible to know what behavior one should expect from rustc means that it isn't a solution. It's another problem. You should check out Ken Thompson's great speech on why this is an issue. https://www.cs.cmu.edu/~rdriley/487/papers/Thompson_1984_Ref...
Or do you think it's wrong to regard unauditable enhancements to free software paid for by Google with suspicion?