I find this well meaning, but mostly incoherent. The fact that implementations are essentially required to interoperate with other fielded implementations is p

I find this well meaning, but mostly incoherent. The fact that implementations are essentially required to interoperate with other fielded implementations is pragmatically true, regardless of any principle. Older versions also don't go away even if newer versions are created. We will still need bug-for-bug interoperability even in a world without the "robustness principle". The main remedies proposed are largely about the setting of the standards themselves, rather than the implementations. Active protocol maintenance, extensibility and virtuous intolerance are things that must happen in the standard. The robustness principle applies to implementations, not the setting of standards.