I read Virginia's State Constitution and the parts related to executive power and restoration of voting rights make no mention on how they must be restored. The thing about these relevant Constitutional clauses is that they are remarkably short and simple. There is no vagueness to it. It doesn't restrict the governor's power at all, in any shape or form, and doesn't even hint at how it must be used. The only overt restrictions I found said that the Governor may not pardon himself if impeached, and that the Governor must report to the legislature who it pardons/restores rights for. Maybe restoring rights en masse like this is wrong, but just because one doesn't like it doesn't make it illegal or unconstitutional.
Our Constitution also establishes a presumption that voter eligibility categorically excludes felons. The Clause allowing the Governor to restore voting rights exists to create exceptions to a general rule. The Governor declaring that "now and forever every single existing felon ever and ongoing until I leave office does not face the constitutionally mandated restrictions" is clearly reversing the constitutional presumption rather than carving out exceptions. Unilaterally dispensing with the law is strictly prohibited by the constitution, and for good reason. I mean, do you really think there would be no separation of powers issues if tomorrow Obama decided in one act to pardon every single federal criminal ever, alive or dead, whether in custody or pending prosecution or sentence served or even people who haven't been caught yet and that this pardon was both backward looking and forward looking? Just because a constitutional power is broad does not mean that there are no clear boundaries found in other constitutional clauses.
Or not. Just because an issue can possibly have multiple good-faith interpretations does not mean that deciding upon one of these interpretations is partisan or made up or invalid. Limits on the executive dispension of law are rooted in history. Noted Democrat and Her's Veep Candidate Tim Kaine argued that he lacked the power to do what McAuliffe did ... how partisan. Muh Judicial Activism!
I don't think its about individual signatures. He could probably get away with a single act if it was just a long list of actual names + crimes being pardoned + Specific Information to the GA. But just saying "Everyone" again is not an exception, its a presumption. So it should at bare minimum mention the names of the actual persons being pardoned, which seems pretty obvious and inoffensive.
