The problem with going cashless is that not many people will be able to embrace it. in the advanced countries this may not be such a big deal as nearly everyone is already familiar with all sort of technology and buying online in a cashless manner. in the developing countries with high number of uneducated people, this can be a very big issue, it will require teaching almost everyone on how to operate an internet enabled device and own one as well.
Going completely cashless will pose a lot of challenges to many people which i doubt the governments are ready to subject its citizens to. So this is not advisable best thing for now is operate in both ways