I will say that the thought into the development of the slope gradient indicator with splatmap generation is super cool. However, my general feeling is that if it's not easy, folks probably won't do it. So, I searched for a simpler solution that might suffice or come close to the original goal. Your wonderful post made me experiment a bit and come upon something that I think others may want to try. Best of all, it's free.
I will show you how to produce this result in Editor without much fuss

1. I generated two textures
A green square (you can download this by clicking the image below and choose Save)

and a Green and white checker pattern
(you can download this by clicking the image below and choose Save)

2. I duplicated my Green layer in the Layers Library and renamed Green (slope)
I added the green square to the first diffuse texture spot and the green and white checker pattern to the second diffuse texture spot
Here are my settings in the Layers Library

3. Changed my Green spline to Green (slope) and recalculated the mesh

Now, had I known this last week, haha, I would have placed that Difficult 2 pin more to the right. You can see that it's probably too close to the edge of the slope.
For this to work correctly, you have to follow my settings above. It is taking advantage of the moire illusion and creating terrain lines. If you make your checker too large (such as 2 and not 0.2), you will not see the Slopes. Image below is incorrect application of layer and slopes will not show.

Anyhow, hopefully, one person out there will find this useful. Keep the CF energy coming!