But specifying everything in grams looks like a practical nightmare for normal home cooks. 0.1g of a spice? Verses 1/4 teaspoon?

You're always free to take an accurate recipe and make it less accurate. You can't go the other way round.

Every home cook should have a digital scale. They cost like $20. And yes, for subgrams, you can always estimate 'a pinch', 1/4 tsp, etc...

By weight is more accurate, almost never exceeds the max of a home scale and simply throwing everything into one bowl, taring the scale each time is quicker too.

Most home kitchen scales have gram accuracy, but I doubt the calibration procedures lend themselves to even that level of accuracy.

Throwing in a bowl works to a point, but if you accidentally dump too much in, you might have a hard time removing the extra 1g.

Honestly, I haven't found many ingredients where you do it to the gram. A few like spices, salt or baking powder you just do it to taste or assume a tsp is enough, for that one item.

A scale still beats measuring cups n things.

It definitely seems like it would be possible to generate something like this in cooklang, as long as you specified everything in grams.

Are these scaling factors baker's percentages? What is the purpose? I.e. what do you use them for? And if these are specified for all recipes, what do you use as the 100% for recipes that aren't based around flour?

They are baker's percentages! The reference ingredient is always set to 100% in the recipe. In the case of the one I linked it would be Chicken, drumsticks.