I don't think it would be VERY hard for modders to add (and would be really awesome if that happened!) but also perhaps developers could consider doing this as well?
I get off playing small countries and this would give me 50 ways of enjoying myself playing these small new countries. I could write roleplay stories about paths to independence of 'colonies' of these countries and the hardships of independent regions that have to be sly to survive near their bigger neighbors.
Some of these territories are empty in the game, but perhaps that is not a problem? It'd be an interesting nice challenge playing as a small, 1.500pop hex colony gone independent xD It doesn't matter if some of them are smaller than a hex - there are many cities in the game that are several times smaller than a hex. Hex is a tool, not a limit.
It is especially interesting where several autonomous/independent regions are near each other, which could open door to a microstate affairs AAR.
I propose a regular modern day 2020 scenario but with small countries/independent regions added. Countries like Abhazia, Osetia, Chechnya (colony?), Ingushetia (low relation rebellous colony), Jewish Oblast (colony), Transnistria, Gagauzia, Nagorno-Karabakh Republic, Åland, South Tyrol (colony), Trentino (colony) Heligoland (colony), Vatican, Monaco, San Marino, Lichtenstein, Campione d'Italia (colony), Livigno (colony), Nakhchivan, Wales (colony), Scotland (colony), Northern Ireland (colony), Gibraltar (colony), Greenland, Svalbard (colony)
Of course they could all be argued, but most could definitely be added, at least as colonies, especially for a scenario that would be designed to play with these autonomous/independent regions.
Would the developers or the modder community be willing to work on this? Or at least on adding several of these countries to the current maps perhaps?