Voidcraft 2.1 includes productivity runes. This is a new feature that I initially wasn't sure if it was even needed, because voidcrafting has no inputs, so increasing the speed also increases the products you get. I decided to add it because a productivity bonus, unlike speed, also uses less input resources, such as void flux. I'm still tweaking the balance; a productivity rune is not going to be as good as an equivalent speed rune, but (unlike productivity modules) it doesn't include a speed penalty. Productivity runes are only usable in recipes where they would matter, so normal voidcrafting (with zero inputs) won't use them.

In heavily (speed) beaconed setups, productivity modules in the crafter can actually increase output better than speed modules. Since productivity is multiplied with speed, there is always a speed threshold beyond which a small productivity boost is better than a big speed boost. In other words, there is actual a use case for productivity modules even without input (e.g., vanilla pumpjacks on a depleted field).

I actually hit this limitation whilst trying to make beacon-heavy primiste plant. I had a circuit-controlled switch between normal and coherent recipe depending on the supply of coherence tea. That ended up sending the productivity runes to the trash slot when downgrading to the normal recipe.

Point being, I think that there is an argument to allow productivity runes also in normal void recipes, even if they take no inputs.