While they can certainly penalize sites that optimize today with respect to the criteria of yesterday, that effectively just means changing the criteria of ranking. Nothing stops site owners to optimize with respect to the new criteria tomorrow. The full implications of the proposition are reminiscent of Russel's paradox, or worthy to be included in a next edition of Hofstadter's Gödel, Escher, Bach book.
Well no, it's clearly stated that the goal is to even the playing field, not change the rules. If SEOs build too many backlinks (and for big keywords you need them in the range of hundreds of thousands) they will get punished. What are they gonna do, build less backlinks? This is of course over-simplified but it does come across as a sound solution.
EDIT: small clarification