And yes, technically countries are not buying bonds, but selling bonds to the ECB. But the ECB is acting on behalf of the countries.

Finally, I expect most immigrants that have a proper education & perhaps money would prefer to e.g. the USA. Increasing immigration as a solution to an aging population is also something that, in the long run, is not sustainable (for many reasons, including ecological). It's time with think of other solutions and perhaps Japan will be able to lead the way in this area, in the future.