I think it would be a much more meaningful article had there been a link to the decision. If there is one, it was well hidden. It seems the grounds are thet the Governor had exceed his powers. I some particularly disturbing language in the decision at: http://www.courts.state.va.us/opinions/opnscvwp/1160784.pdf
"Never before have any of the prior 71 Virginia Governors issued a clemency order of any kind — including pardons, reprieves, commutations, and restoration orders — to a class of unnamed felons without regard for the nature of the crimes or any other individual circumstances relevant to the request. To be sure, no Governor of this Commonwealth, until now, has even suggested that such a power exists."
The Virginia Supreme Court has based its decision on equating restoration of voting rights with 'clemency or pardons, etc., all of wwhich actively affect the incarceration and fulfillment of a sentence, rather than something imposed after the convicted has served hie/her sentence completely. Sounds like seeking a reason for a political decision as it seems equally valid to argue that those other concepts have a unique characteristic that remove those issues from the issue at hand.
The governor says he'll do it individually which is permitted.
I wonder just how many, if any, of the court's justices were appointed by Kaine.