You make the assumption that the hw-independent work finishes with the parsing and any and all possible optimizations are only hardware-specific. This assumption is false and that makes your reasoning, which is based on it, invalid. Typically the hw-independent optimizations are more expensive and time-consuming the hw-specific ones. But giving you lectures on compiler optimizations is beyond our goal here.
At any rate, the suggestion was not directed to some random guy from the internet, which neither can make additions to the opengl spec, nor can be expected to even know what he is talking about. It was directed to hw vendors/khronos, which should know their stuff and can appreciate a suggestion if it is any good.