Yeah cashless is the way to go, but I dont think the problem is as big as it seems. People are also becoming digital nomads, and while citizenships for pay, and more importantly the digital identities that come with them, are still kind of expensive, long term I expect it will become cheaper and more common.
This also directly solves the issue of op. Cryptocurrencies are a stop gap solution to this, but known transaction histories and inherently poor fraud prevention make them poor digital cash replacements. Today Ecuador is shilling bitcoin, but imagine if they instead sold tier 2 citizenships, no taxes no welfare type, with new and independent identities. Pay 5000$ and get a new identity and passport, along with an account in one of our many banks, or which can be used to set up an account in an international bank. Sure you wont get to share credit scores with your main identity... Various international laws mean it wont be called exactly this, perhaps its a fee for the creation of a minimum accounting requirement corporation with hidden controller instead (and trying to prevent these is already ongoing but it does not work), but it does not matter in practice. As long as it satisfies the conditions of being able to make transactions easily, has a dispute mechanism with centralized authority with the self serving interest to remain independent, etc.
I'd wager that the majority of identity thefts arent performed in order to steal money from that identity or ever even cause any damage to the original identity. They are performed in order to get around travel and work restrictions. Lets say you are from ukraine or belarus, now getting a work visa equivalent to germany or france is kindof a pain in the ass, in particular doing so quickly, but buying a stolen passport from e.g. rumania isnt hard, and all you are doing is setting up a single french debit account in that name and working under that identity. Odds are that kind of thing gets discovered 30 years latter when the original identity realizes they are getting a small pension from some job in france they never had. But why would they care.
Massively expanded surveillance states could prevent this, but while that will be the case in china, places like the usa are just to discoordinated, and the eu is actively working against it to the point both google and facebook are no longer asking. How can we make our ads better, but rather how can we keep ad quality with much less information per user.