It wouldn't necessarily need to be in-road, but there are numerous places where you could adapt. For instance, cats-eyes in the UK (retro-reflective markers) are placed on virtually all motorways at lane boundaries and the car could look for a signature from them (I imagine at night, autonomous cars already use them as a feature for lane boundary detection). Nobody bats an eyelid about re-setting cats-eyes every time a bit of road is replaced. You could also put boundary markers on either side of the road, in the central reservation or something similar.

The idea would to put the smart tech in the car. What's going at the roadside could be made very cheaply and integrated into existing features without needing to rip up the entire road.

Other countries have toll highways which are well maintained, that's another option for installation.

I don't see this happening in rural/country lanes, the cost would be obscene (but again, we do liberally use reflectors in the UK). I also don't see this as a panacea, it would simply be a backup in horrendous weather.

I've seen those cat eyes before, but never in locations where plows have to travel. They are also relatively easy to place, just requiring some tar and a manual "pick & place". Making something plow proof would require embedding it in the road, either with a drill or a "rumble strip" like divot.

Yes. Smooth, flat, pothole free tarmac would be nice.