Denmark's Oyster-ish system covers the whole country. Anonymous cards need a balance of at least 70kr to start a journey, and are limited to a region of the country — e.g. Zealand (Copenhagen's island) and nearby small islands. Adding the non-refundable cost of the card gives an amount larger than the longest journey within that area.
It's possible to set an anonymous card to a high advance payment (600kr = 80€), and then use it to travel across the country.
Great Britain is significantly larger, has much higher train fares, and isn't neatly divided into islands. They could limit it to contactless credit/debit cards, but I don't see a neat way to extend Oyster over the whole country.
The reality is that in the UK as many other places in the world, public transport is highly subsidized. All these little transport fiefdoms and zones aren't accomplishing anything at all. There is no good reason to not have a single payment system.
The Netherlands used to have this system over the full country (OV chipcard) when I lived there (it seems to still exist), the card could be anonymous too.
After the French ticketing system, this felt magical to me.
It's possible to set an anonymous card to a high advance payment (600kr = 80€), and then use it to travel across the country.
Great Britain is significantly larger, has much higher train fares, and isn't neatly divided into islands. They could limit it to contactless credit/debit cards, but I don't see a neat way to extend Oyster over the whole country.