While I agree with Naimark's claim, I don't think that it can should be used as a scale to evaluate work. Between every first and last word is an always-growing, still-significant body of work. If the first word is determined chronologically but the last word is determined by comparison of importance, then there is no definition for what else is notable. The general public may best remember the first and last word artists best (e.x. Beethoven, Pollock, Warhol), but that doesn't void the value of other artists.
The intent to develop first or last word art also creates a dilemma. If an artists attempts to create a last word art piece, then they will work forever and maybe never create a final work unless they are the next Beethoven. As Naimark's article notes, Beethoven's work has withstood the test of time. If an artist works to create as many first word pieces as possible, then their body of work will be rushed and never reach beyond a shallow degree of complexity.