They will just create/steal/borrow/bribe/underpay people who make styles and pretend the (a eye), did the thing then mix and match, tests to add variation and say look it learned... unless they have donated brains in some building underground or something, i doubt they can "generate/script/program" and (a eye) I wouldn't…
Both. You'll probably use vert paint, being cheap and effective way to blend materials, and probably masks, even if it's just a basic noise and gradient material function to break up vertex paint blending or height lerp from a height imput for example. Also don't forget decals on top of what ever solution you use.
Have you looked at Adobe's site? Tons of great resources to get you going: https://substance3d.adobe.com/tutorials?software=Substance%203D%20Designer As just one example: https://substance3d.adobe.com/tutorials/courses/creating-a-tudor-house-wall
There was an example posted somewhere within that Twitter thread- I can't find it, though. They showed the version the generator recreated as something akin to a messed up VHS tape- huge blocks of random colors and structural corruption