The more I think about this 50% floor, the more it appears full retard.
A country switching capital to go overseas is basically pretty much the same as an independant CN.
A native nation that westernized also fits to the category.
This is also arguably true for western nations which moved their capital in Africa, and westernized african/asian powers.
But no, the problem is that, for the devs, Russia should'nt be able to have provinces with more than 50% autonomy in Siberia. Halving all Siberian's provinces base tax would have resolved the problem, but no, that imba solution was chosen...
More than giving the ability to go below 50% to CN (meaning only them can go below 50% right after the province is fully colonized), it would be more realistic to simply disable the ability to decrease the autonomy of colonized provinces, while removing the floor, meaning that only time could reduce the autonomy. Because the dev wanted this floor to translate the fact this provinces have a low population.
This decreasing could vary with the nation's tech group, ideas, and distance of the colony to the capital.