However, you'll have evaded wealth tax for years in case you lived in a country collecting such a tax.
If it's several million dollars worth you are talking about, then that is more than enough money to easily migrate to a country with more friendly bitcoin laws if you are concerned about a wealth tax.
I wonder what has happened in scenarios where people have lost access to their wallets or keys for a number of years (and therefore not paid wealth tax since they don't technically own that money) before managing to recover them, find an old back up, brute force them with newer technology, etc. Have tax authorities gone after them for historical wealth taxes?