Regarding your second point, there's a couple of dozens of countries that specifically require you to denounce your other citizenship to gain theirs, as well as

Regarding your second point, there's a couple of dozens of countries that specifically require you to denounce your other citizenship to gain theirs, as well as those whose citizenship is lost automatically if you become a citizen of some other country. I do see the cases of multiple citizenships (and therefore multiple passports) increasing in the future, but I wouldn't hold my breath for it to become a common occurrence within our lifespans.