This is the same mistake that Yglesias makes--he assumes that there is no constitutional right to vote, and so concludes that creating an
express constitutional right to vote will change the way the courts review voting regulations. But if there already is a fundamental right to vote--and there is--then having the Constitution say so expressly won't change anything.
If what you want is to make felon disenfranchisement unconstitutional, then you should seek to enact an amendment that plainly says so, for two reasons. First, nobody likes a person who hides his or her true intention. Second, simply making the pre-existing fundamental right to vote express in the Constitution (probably) won't accomplish your goal; you'd need to be more specific. (This is especially so since abridging voting rights on account of a crime committed appears specifically permitted under section 2 of the 14th Amendment, as the Supreme Court pointed out in 1974 in
Richardson v. Ramirez.)