Thompson implementing his attack as a compiler attack is a detail, primarily
because source code was the normal form of software interchange but the
basic compiler toolchain obviously still required passing around binaries. In
short it was the *only* place he could have implemented an attack by
subverting binaries. His paper is explicit that the compiler attack is merely a
demonstration of a more fundamental problem of having to place trust in
computer systems. Particularly, he mentions microcode as a possible level of
attack - clearly a completely different thing from compiler level and indication
that Thompson was making a very general point.
To think that Thompson's attack is only about compilers is surely to miss the
point of a classic paper.
Also, I don't expect clairvoyance. Indeed, you miss my point about which
direction the attacker is going.
I think perhaps I should properly write up my criticism...