The hard part has always been getting it out and not getting caught.
Nothing is truly yours.
Courts have centuries of case law for how to deal with people that hide assets from judgements. They're not going to care whether your assets are in a shell company or a cryptocurrency.
Where they are much better than a hole in the ground is when it comes to moving your assets to a different jurisdiction. As long as you can physically get yourself from Somecountry to Othercountry, all your e-cash will be accessible in Othercountry regardless of what Somecountry may have to say about it. And even if Somecountry imprisons you, you can still hand over your e-cash to someone else with a single message.
I can't think of any asset that offers that particular advantage.
You also can only pull this trick once: after you are a known flight risk the next country to come after you will be careful to make sure your detainment comes as a surprise.
Finally, as much fun as it can be to game out, for how many people in the world is this use case actually applicable?
Think instead of an ordinary person fleeing a disintegrating economy and/or an oppressive regime, who had stashed away some e-cash for such an eventuality.
It's also possible that the government may declare some bills invalid (what happened in India with larger bills). Also, government could inflate away your wealth by printing more currency.
You make mistake of assuming that countries won't put up a global firewall that makes bitcoin/ether network impossible to operate. If China can filter traffic at internet scale, crippling Bitcoin network even if say EU/US/China are on board is trivial.
Currencies are backed by the only thing that matters, its will/trust of the people. And no amount of crypto changes that. Unless of course you have some magical way of baking silicon on your own into processors and other chips used in computers and networking equipment in your backyard.
Bitcoin/Ether barely register in terms of the total economic activity (75 Billion $). With significant fraction unusable. They will either be tamed or destroyed.
In fact another way of looking at cryptocurrencies is as a revolt against the Visa/MasterCard duo-poly & regulations that has made digital transactions too difficult. The moment digital transactions become cheaper/more-efficient, the allure of crypto-currencies will disappear.
As for the allure of cryptocurrency, only time will tell. I predict they will continue to grow in prominence.
Except for drugs, contraband, money laundering, and evading capital controls. Which, from day one, has been the entire actual value of these things and remains so.
That's a reasonably big business to be sure, but it will always remain a niche element and always be under fire, for obvious reasons.
Plus as more avenues for directly using bitcoins opens up, the 'getting it out' problem becomes a non-issue. Plus, mixers!
People forget that, for that money to have any value, you eventually have to interact with the rest of human society. As another commenter said, we've been dealing with this for centuries--black markets, cartels, smugglers, etc. Everything old is new again.
Real cash is much more anonymous than stupid blockchains where every single transaction is published globally for all time.
You are right the web is tracked so even if Monero itself has untraceable transactions, buying Xmr generally requires an exchange which in turn kyc.
Wait - does that mean you could literally get off on a technicality?
I would advise not storing anything having to do with your Ethereum private keys in a Github repo.
Beyond that, if we're speculating, a world where all transactions live on a blockchain is an ideal one for a government bent on tyrannical control of the economy. It is likely that governments of the future will have advanced methods of associating wallet activity with real-life activity, especially for citizens who intend to interact with the larger law-abiding economy (if you ask me, blockchain money is the ideal currency for a tyrant). Of course, you can just continue to speculate about future crpytocurrencies that will solve all these issues and that is the reason why this type of speculation gets us nowhere.
Yet. Everything needs to start somewhere.
Eventually, someone asks the question, "Why can I buy weed with Bitcoin, but not pizza and chips?" And delivery of munchies is a legit business that can be advertised. Once recognized as a viable model, it can then be poached by major corporate players as part of a local pilot program, which can then be rolled out to larger jurisdictions.
The problem, as usual, isn't that you can't buy anything with it--it's that you can't buy everything with it. As long as you can't pay your electric bill with cryptocoins, the business that accepts one as payment can't also pay its employees with that same cryptocoin.
Honestly, would you even apply to a job posting if it said salary to be paid exclusively in Floopcoins?
And in Europe one already can pay electric bill and pizza with crypto. While only few utilities already accept them directly, many more enterprises want to establish themselves on this emerging market by mediating these transactions.
Better yet, I'll get you a printer and you can print me some transferable bills.
LocalEthereum.com is being developed too.