You're mixing up multiple problems. If adding problems is what you want, none of my highschool classmates called each others in the "John" part of anyone's names, and emails beginning with a "Hello $firstname" in my language sounds weird to me anyway. But first/last names are often reused for billing and official purposes, so East Asian(CJK) users would know to fill the "first" with given and "last" with family name if asked that way for official purposes, no matter the visual order or how will it be used. If it's not for official purposes, people are just going to throw in random junks anyway.