You open a Coinbase account. You have bitcoins on there. You don't touch them for 5 years. The government forces Coinbase to follow their existing escheatment laws and send them the money (assuming you are a resident of NY). This already happens with your bank accounts. I had one with a few bucks in it that I hadn't used for years. They sent me a letter that said in 60 days they were sending it to the state. I had to call and "reset the clock".
Obviously, nobody can seize bitcoins that you hold yourself.