His point seems to be that there are reasons in principle you cannot do this (holding the design fixed). It's a little like making a type system turing-complet

His point seems to be that there are reasons in principle you cannot do this (holding the design fixed). It's a little like making a type system turing-complete then saying, "we can fix the halting problem in a patch". If you change the design, then you can fix it. This is what I interpret "design flaw" to mean.