"Real grass" for the Nurburgring

As a 3d artist myself, what i would try is putting some "3d grass" behind the guardrail at some places like on the left of the image:

but the challenge would be to distribute it evenly with some kind of tool and have the fins go upward even when the ground is steep,
not have it clip with anything, not have it hover over the ground, and other things.
there also has to be a good color transition between grass and terrain, otherwise it will not look like the grass is actually growing from the ground and it will look more like glued on.
also grass is not just grass, there are dozens of different plants wich all grow together and some grow in spots and have different color and than others, some spots are brighter others more yellow.
so you need grass models with different grass textures on them and not just place them randomly across a surface but place the different grasses together in spots.

of course there are tools out there wich are built into the software you are using or if not you just buy them.
But in a game engine everything needs to follow very specific rules, for performance reasons, so you might need to make your own grass tool.

i am sure s397 does experiments with 3d grass and tests if the effort and performance penalty is worth the additional visual fidelity, and nordschleife might be a case where it actually makes sense (directly behind the guardrail at some spots on the track for example) but you never really know until you try it out.
also the grass needs to fit in with the average level of detail of the track and not look more detailed than the rest, because it would make the rest look bad and break immersion,

these are just my experiences with 3d grass, i might be wrong a bit, who knows