I have looked into this sort of approach in the past and concluded it doesn’t really work without a full history planet, unfortunately. And when you have to process a full history planet on every map update just to work out whether a highway is actually a road or not, something has gone very wrong somewhere.
What I’d really like to see is a bulk edit of rural highways using something like this. That would go further and faster to fix the problem than pretty much anything else. Generally I’m of the school of thought that bulk edits hinder the development of community, but when it’s been 17 years and there’s no sign of the problem getting sorted any time soon, I tend to think desperate measures are needed.