The Jim Crow era may be over, but all the myriad guises of voter suppression is still very much alive. It may well be, today, a sliver of what it once was, but that says far more about how pervasive and institutional it once was than anything else. It still is very much an active ans serious problem today. This is not some relic from the past but an active law that today is protecting and preserving the Constitutional rights of many voters across the U.S. Shelby County, AL, one of the plaintiffs, has even just recently been cited for various voting rights violations.
States and municipalities were singled out arbitrarily but rather, because of endemic and pervasive voting rights violations. Nor is this some permanent Scarlet Letter lingering from a bygone era. States and municipalities can come out from under their voting rights Act obligations upon showing a history free of violations. Should they continue, today, to violate, as has Shelby County, then they rightfully and duly remain under its obligations until such time that they evidence due regard for voters rights. The "equal protection" clause of the 14th Amendment adheres to individuals, not states or localities per se. That these states and localities were, and still are, violating individual voting rights guaranteed under the U.S. Constitution, it was and is entirely appropriate for the federal government to assure that these individual's rights are duly protected, hence the Voting Rights Act.
I would agree with Rapier that it would be undue judicial activism, to borrow that rather vague phase, to undo an act of Congress that was just very recently overwhelmingly reaffirmed (2007?). SCJ Scalia had some rather disturbingly broad comments impugning the motivation of Congress in reauthorizing this legislation with vast bi-partisan majorities that would open the door to the SC passing judgement on pretty much any legislation based upon presumption of malice in motivation alone. Any ruling should be far more factual and hinge solely on actual violation of the Constitution. I don't think there is, and that the Voting Rights Act is still a current, viable, effective and Constitutional piece of law, but its the opinion of nine other folks that matters.