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
The first impression I got after reading OP is this. EU and USA are not the whole worlds. There is a vast area of land in Asia, and Africa where people don't have an internet connection and are out of the digital landscape we live on. Paper cash is still the only way of the economy there so if mass adoption of cashless policy has to be taken then there should be some measures taken for those people.
On the other hand in many urban areas internet connections is not that strong and secure. A cashless economy means no paper cash. So any disruption in internet connection would cause major damage to the economy.
Inequality is always the thing to be considered despite all the benefits when moving from a cash to a cashless society. From all I know, old people hurt most since some of them also didn't know much about smartphones to use it as e-wallet. Wireless or broadband internet connection like you mentioned also a problem since if we can't access to it, we will be stranded from the grid with no alternative?