Looking at Liana, the bootstrap works by compiling an older rustc with mrustc and then compiling newer rustc with the compiled older rustc, right? So technically it is bootstrappable.
So that means that there is a way to review the entire chain. Hopefully someone is also doing that.
rustcwithmrustcand then compiling newerrustcwith the compiled olderrustc, right? So technically it is bootstrappable.