I've seen this topic before. It wouldn't be my choice.
In some cases I've encountered urban neighborhood roads without road markings, and they're generally fine.
For the rural roads, we have DITCHES, and in some cases vertical dropoffs (something not shown in most of the photos above).
Mom's road might be a good candidate. Low traffic, the occasional cyclist or pedestrian. And VERY NARROW. Personally, I like to drive on it with the left tire just to the left of the center line.
However, it has several issues that make it an emphatic
NO!- Get your lane positioning off and you're in the ditch, or taking out mail boxes. Thus, when traffic comes, I like the center lines to aid with lane positioning.
- Corners are very crisp right angle corners which are mostly blind. I've driven on one lane roads from time to time, and the rule is always be to the right when going around a corner or blind area. This "Advisory" marking would tend to encourage drivers to take corners, hills, or other dangerous areas dead center which is very dangerous for them.
- There just isn't enough pedestrians or traffic to really make it an issue.
The other issue that I've brought up from time to time with discussions is a human performance issue. If one makes an error in judgement, it is much easier to move right or left one foot or so, than pulling over a full car width. And, you have to trust the response of the oncoming traffic too.
I can't imagine trying to convince people that 20 MPH is the appropriate speed limit for roads that formerly had 55 MPH limits.
Edit: Oops, Cat posted the response.