Can cryptocurrencies be reliably taxed if everyone adopts them?
If we didn't use fiat currency then how could governments function?
There's plenty of evidence most people can't/don't want to do full self custody. So if "everyone" adopts them they will inevitably have the coins managed by third parties. Plus everyone including many people with self-custody have expectations about fair conflict resolution and fraud prevention. Even if they are in denial till stuff hits the fan. That's where and how governments step in.