Will Voter ID ever hit the Supreme Court?
It already has. SCOTUS has approved voter ID in Indiana.
The other cases mostly trace to Section 5 of the Voting Rights Act, wherein the Department of Justice retains right of review over any changes in the laws affecting voting in 15 southern states.
Holder has challenged voter ID laws in several of those states. The court has already reviewed the South Carolina case and shot down the DOJ -- but the delay meant that it couldn't be implemented in this electoral cycle. Which is all Holder wanted, anyway.
In any event, voter ID has already passed court muster.