Given the current last-in-first-out crafting system, the micromanagement of inventory space during bulk crafting is incredibly tedious and taxing (stacks are unusable during the process, so some inventory functionality is already lost). This problem also leads to many confusing interactions for new players as they learn the system, discouraging them from interacting with the system.
Two main examples, though not exhaustive:
Autumn Steaks with mixed mushrooms
Measured Distillates, Lye Ablutions and Fiery Combustions all crafting in on themselves (Think Lye Ablution accepting Lye Ablutions as an alchemical ingredient and you'll understand)
Why a separate mode?
The proposed solution I made in the livestream is essentially a crafting precision mode. The reason is that sometimes, it's easier to have the indiscriminate crafting like we have today so we should retain that functionality. However, we should enable the other use case as well to help with the problem statement above.
How does it work?
The Precision system would be an in-crafting UI toggle that breaks the recipe into all of its components within the UI. So in the case of Autumn Steaks, it would break the mushroom(x2) icon into two separate icons of the variable mushroom within the UI. Clicking and dropping an acceptable ingredient onto the icon would replace the icon with the ingredient's icon, locking in that selected ingredient. You should be able to do this for all ingredients that are variable while in Precision Mode.
Now I'm no UI/UX Engineer by any means, so this can definitely be up to the implementer. That being said...
Proposed UI Mock-up to Illustrate the Flow:
Precision Mode Off (Current default UI) + toggle

Once the user toggles Precision mode, the recipe breaks out into its components (ex:no more mushroomx2), allowing the user to click and "drop" (won't actually drop, just changes the icon to show selection) any applicable ingredient in the correct box.
Precision Mode On (Ingredient Selection Mode)

Edge Cases(will add more as feedback roles in):
1. In the event that a massive variable recipe is ever created, UI could become cluttered.
2. Variable liquids? (Can you even do this? Thinking like Nectar vs Honey in a Sweetener recipe. In this event it'd have to be binary, or rather one or the other.)
3. Running out of one of the ingredients should stop crafting, return the error for lack of material to craft.
4. Maybe not everything needs a precision mode? Does it actually effect anything if we allow it on everything?
5. Recipes with distinct ingredients should not change in precision mode (EX: Big Bear Banger utilizing either Pork or Boar meat, however Bear meat is static)
6. Would not apply to what individual ingredients are made out of (butter made from cows milk vs goat milk). Thought I should call this out.
Feel free to tear it apart, I just want to see this age-old crafting system get some love. It's been practically the same since Legacy.