In the UK you can get sentenced to prison for up to 5 years for not giving up your encryption keys. I guess this law would work for those not giving up their bitcoin private keys as well. Once you have spent 5 years in prison they'll just ask you again, and if you still refuse, back you go. They may not have your bitcoins, but they will have your freedom. Luckily this fascism hasn't spread to many countries yet, but the trend is there and it wouldn't surprise me to see this implemented across the world.

From my understanding it don't matter if you "forgot" the key.

Oh and brain scanners are also making good progress, it would be foolish to believe government won't use them for "SERIOUS crimes" once that becomes viable.