Japan has always been the number one country in Asia in terms of technology, bitcoin was also born in Japan, so I wasn't surprised to hear that Japan will have its own crypto currency
Yes, it can surely develop its own cryptocurrency and they are working on it in response to facebook’s Libra but I read somewhere that there are certain hurdles that they are facing in there way so they first have to deal with them. But as you said that they are on the top in the development of technologies, they will soon deal with their problems and Japanese digital currency will be in market.