I can’t speak to that with any degree of certainty because things are in flux seeing how we’re not even in beta.
I have zero horses in this race regarding Shadow. I don’t play Shadow, so whatever happens to Shadow is outside my realm. Shadow could be completely retooled to something that’s neither voidform or shadow orbs and it wouldn’t affect me.
That doesn’t change the fact that voidform isn’t impossible to balance. Is ramp-up too long? Shorten the ramp-up. Is the voidform not impactful? Improve the rotation or haste stack bonuses. Voidform too long because of the shorter ramp-up? Shorten the voidform and make it stronger to compensate. Even at the highest level, you can tweak.
And quite frankly, it doesn’t matter whether Blizzard gets it wrong. That just means they got it wrong, it doesn’t mean that voidform is an impossible-to-balance design.
I hate to break it to you, but a lot more thought goes into classes and specs than you likely realize. What you think of those classes and specs is irrelevant. Specs don’t get made with the intention to only last 1 expansion.