Regarding Void Form being tweaked into a much forgiving iteration.
So for those of you wanting to keep the insanity mechanic. How about this.
Take the Demon Hunter Demonic Mechanic where upon using Eye Beam, you go into a Demonic form for 5 seconds. What this does is limit you to a short but guaranteed duration.
So lets apply this concept to the Shadow Priest / Void Form.
Max level TalentVoid Form : Activated by casting Void Bolt (Cost 5 Shadow Orbs). Twists your Shadowform with the powers of the Void, increasing spell damage you deal by 20%. Granting an additional 0.5% Haste every 1 sec. Lasts 5 sec. Mind Blast increases the duration by 2 sec, Void bolt by 5 sec.
How this works:
Once you enter Void Form, you now have a very short window of time with an increase to your spell damage and more and more haste. You use Mind Blast to extend the duration as much as possible and once you get 5 Shadow Orbs, you can use Void Bolt for decent damage and extend the duration by an additional 5 sec.
If badly played or poor gear or a mix of both. You should be able to have 2-3 Shadow Orbs at minimum once Void Form fades and then only require around 10 sec to get back in again. Or snipe some Shadow Word: Deaths and get right back in as soon as you got out. But doing this, you loose out on the stacking haste gain. So you want to try to stay in as long as possible but its not too much punishment if you fail to do so.
You will no longer need to ramp up as quickly/much as you can easily build Shadow Orbs with a mix of Mind Blast, Shadow Word: Death & Auspicious Spirits (if talented).
tldr
Your Void Form has a constant duration based on your actions aka buttons you pressed. Not an ever increasing struggle to do more and more and more in less and less time madness.