I've always wanted to do that, but the dirt runways in the old scenery had a bug in the uv-mapping which is now fixed - so in recent GIT you can now enjoy procedurally textured dirt runways.
Here's an example where I let some grass patches from the airport green leak into the runway proper, and put some wet puddles on.
Ultimately, they'll be regionally configurable, so we'll have true sand strips in the desert.