I don't think it would be enough to encourage people to move to the country. It would just have to be enough to not overly penalise those who do.
And that doesn't even necessarily mean completely rural. The village where I live has one shop (part of the garage on the edge of the village). The next nearest are all about 3 miles away. On my daily bike rides, I normally ride through several other villages, and very few of them have any shops at all.
This is the trouble: the lack of facilities are often because people drove to the next village because there was a cheaper shop, and it snowballed from there. It's not quite as bad here but we see the same happening.
Arguably this means that as you say, the absolute limit has to be to not make it harder to live in a rural area, but not subsidise car travel. At the same time, local or regional investment in facilities and other local transport options are essential.
After cycling to my new job for a couple of weeks in summer I realised it was only possible for me to take the job because of a 5km section of cycleway alongside the main road, which means I can cycle safely between my village and the next on the most dangerous section. If it wasn't for that, I'd be unemployed.
This is the problem in a nutshell: we have to provide alternatives so people don't need cars, not demand that cars have priority over everything else and call it "giving people a choice".