"Thanks to the EU/EEA, anyone can legally migrate anywhere within the participating countries (only exception being Croatia these days), and I don't see Switzerland or Norway being that much more welcoming than Germany to immigrants these days. Sweden has been taking on many immigrants from outside of Europe (and continues to do so, e.g. from Syria), but publisher counts are still stagnating."
Welcoming to immigrants: depends on whether they come from outside Europe or not. Sweden with stagnating numbers - but the majority of immigrants come from Syria, Iraq, in short Moslem countries and not much increase can be expected from these nationals. Norway has a huge immigration from Poland and Lithuania, and has an increase partly due to these nationals. Close to one in eight publishers come from these countries. Poland, Hungary, Czech Republic etc experience a stagnation and even decrease in the population and therefore have a very ageing population, because the younger ones leave for the wealthier European countries.
One has to look at the population development of the countries in question before making quick comments. Japan has a very much ageing population and will decrease hugely during the years to come.