Dear Tom, it seems we can measure the difficulty by the variety of answers.
In my opinion, trying to split complicated Europe in yet local geographical entities could end being difficult.
The Scandinavian/Nordic point, and British Isles anecdotes are only the beginning, some people are really sensitive about it...! I am pretty certain a "basque section" will meet some pushback from the Spanish and the French sides, whereas you'd have to exclude Hossegor which is 20 mins up the coast from Biarritz airport, as it is not Basque. Or include it and hear their reaction as they are Landais!
And that's probably nothing compared to the Balkans!
I think you are right: it's much safer to stick to large groups of countries, and have a section of the book with maybe coloured maps or itineraries showing the cross-borders clusters that you can visit together from practical airport or train station hubs as someone mentioned.
Doing just country per country seems to defeat the purpose, and might have people miss opportunities like Pas-de Calais with Benelux, or Chantaco with Hondarrabia. I see your point.
So the best seems to me to adopt Cristian's plan. Sounds perfect. Especially as it sticks to the style of golf you encounter. Including dropping the Alps section where I think he has a point too.
What about a section called "European Islands"? Jersey/Guernsey (with the Granville option), Canary Islands, Balearic, Cyprus, Sicily, Madeira etc.
Good luck!