Today I came to think again about on-demand bus service areas. There is one mention on the OSM wiki: this explanation from Belgium, but I’m not sure if it really refers to a service area rather than a line with on-demand stops. The idea of the on-demand bus service area is that from one central stop a small bus will take you wherever you want to go, almost like a taxi, but only at certain times, and together with other passengers (if there are any). The concept has been quite common for some time in rural areas all over Europe. In my opinion, we could just draw the area, give it some tag so it is put down in the data that this rural area is generally accessible by public transport.
The reason I came across his edit was that my wife and I had a day off and used it for a bike ride through the sparsely-populated area north-east of Wolfsburg, just across the former border between West and East Germany. It was nice cycling along the Mittellandkanal - but I have to say that we are quite used to gravel tracks and have equipped our bikes with appropriate puncture-safe tyres. Some excellent pear trees along the road here. No traffic at all because of a road closure further south. When we came to the nearest larger village, we had to decide if we wanted to continue on the road in heavier traffic now or use a track running parallel. To our surprise (it wasn’t mapped as such yet), it had excellently smooth asphalt. For the way back we had opted for a bus line that also carries up to five bicycles (for free!). It’s really amazing what the land of Saxony-Anhalt with its limited resources and sparse population does for an attractive public transport. Lower Saxony could take a page from its book!