I think that Speed Baking III is made totally unattainable by the Prestige Update as seen in the Beta. Indeed, once the first heavenly upgrade is purchased (and the season switcher is now heavnely!), there is no way back. The only way to get any Speed Baking shadow achievement is through hard reset. In my opinion, it is a problem.
Here is an attempt to solve it. I think there should be a heavenly togglable allowing to switch on and off the heavenly upgrades. Or, better, maybe something like an upgrade to enable them all. For example, while the heavenly chip secret would still enable the heavenly cookies multiplier, a new upgrade would appear upon buying your first Grandma, something like "Grandma's Testament", allowing you to "inherit" from your legacy of heavenly upgrades. After each ascension and as long as neither the heavenly chip secret nor Grandma's Testament are purchased, the Speed Baking achievements would lie within reach.
This could also make a new grandma type appear (possibly not until the 15th ascenscion and/or the purchase of a new heavenly upgrade?), like Ghostly Grandmas, Ascended Grandmas or Heavely Grandmas, watever they are called.