I didn't mean loading/unloading on the fly, I was talking more for when you leave a track and come back. So, you were closer with the previous assumption of textures spanning the track, and you are completely correct, it would be large textures - depending on resolution. I didn't exactly mention negative side effects, just a thought. For a track like Fern Bay Club, Aston Cadet/Club and so on I think this would be reasonable, but certainly for tracks like Aston Grand Prix there would be a considerable surface area to cover. The other good thing though, is the memory for the texture could be something like 4bits, or at the highest of 8bits. The skid mark texture really only needs an alpha channel. Which would save considerable amounts of memory - so I do believe this is a plausible idea. Remember it would only span the track portion of the environment, certainly still a large area, no doubt. Also some texture streaming techniques could do this, requiring a bit of work and thought - certainty.
I know it would work on my card, but I am also quite sure it wouldn't work on the low-end cards that LFS supports at this time.