Roads are currently built in MSL space (that is, absolute elevation on the planet) and thus don't change when the base mesh changes. In a previous post I discussed the idea of having them be AGL based (draped) so that they would "hug" whatever base mesh you have.
First I should say: this isn't coming any time soon and won't be in 9.0. But also, upon closer examination, there are a number of ugly issues just below the surface. Consider all of the things that the global-scenery generator does with roads:
- Road type is selected not only from source road data, but from surrounding conditions, some of which are not obviously determined by the final DSF.
- Road bridging is determined based on nearby roads, water, gradient constraints, and available bridge templates.
- Road type is further influenced by bridging considerations.
- Roads are smoothed to try to build the most even access, "hiding" rapid changes in underlying terrain from a high-speed roadway.
- Powerline tower locations are picked from terrain peak to peak with constrained maximum lengths. (The individual segments also controls the span of wires, so introducing new nodes in the draping process might be undesirable.)
The eventual solution would be to do all of the road processing in X-Plane while draping - but this implies that the author of a custom road grid doesn't actually have control over how the roads come out. One advantage of the current system is that total control over the roads is provided in the DSF - given appropriate tools, a modeler could very carefully hand-craft the roads with a lot of detail.