I don't think that's necessarily the case. Rather, the Second Amendment can be seen as vague, yielding several interpretations, especially in light of its ungrammatical "prefatory clause".The Supreme Court's current interpretation of it effectively ignores that clause; the notion of a "militia" simply doesn't enter into its reading one way or the other. The Founders' intent is unclear, and Stevens is proposing to clear it up... in his direction.
Now that the Supreme Court has spoken, it becomes the law of the land. If 500 Floridians had voted differently back in 2000, maybe the justices would have spoken differently, but they didn't. So now, the only way to change the interpretation of that baffling "militia" clause is to change the wording.
Which is a notion so utterly quixotic that I can't imagine why Stevens is wasting his time penning the editorial. In fact, I'd go so far as to say that it reinforces just what you said: since there is less chance of altering the Second Amendment than there is of me flapping my arms and flying to the moon, the current interpretation will stand. Whether that's what the Founders intended is irrelevant.
(And given the changes in what "arms" are over the past two centuries, I don't think that's unreasonable. What's unreasonable, sadly, is that the divide is so deep among Americans, and the legislative processes so focused on stasis, that there's absolutely no forum in which we can meaningfully discuss the possibility of change.)