Husband and wife have the same surname in Japan. The majority of couples take husband's last name. The survey in 2012 showed that 95% of married man keep their name and 5% changed, up from 2.6% in 1995. The law for the same surname for married couple that stated in Meiji period came from the tradition of family business. But some women claim that they have troubles due to the change in their surnames. Now there is a movement for married couple to retain their last names after marriage.
Even in the US and some Europeean countries where gender equality is more advanced than Japan, the majority of married couples take husband's last name. The recent survey of married and single people in the US showed that 92% of men kept their last names, while 5% changed their last names and less than 1 % hyphenated their names with their wives' last names. On the other hand 80% of married women took their husband's last names, 14% kept their own last names and 55 hyphenated with their husband's last names. These numbers for women reflect their age and education, 9% of women ages 50 and older kept their last names, in comparison with 20% of women between 18 and 49. And 26% of women with post graduate degree kept their last names. The same surname in the US was decided by law when people immigrated long time ago.
In the light of the situation in the US, I think that even if the law passes, it will take some time for separate surname to become common in Japan.