Thank you all for participating this discussion.

Let me explain why I think it's important to have a key recovery mechanism with BTC. And I understand all privacy concerns, that's why, I see all proposal here as optional, but most likely suitable for large scale BTC adoption.

Assumption: For the majority of people around the globe, the smartphone will be used as a wallet. There are people using feature phones to make BTC payments already, because they can't afford a smartphone. So probably, not all can afford to buy another hard wallet, and have the possibility to store this wallet securely.

Scenario: Imagine some people living in Asia 2004, having stored their BTC on a hard wallet, as every Bitcoiner suggest to do, maybe they also have some paper backup.
Within minutes, a Tsunami arrives, destroys your house, you are losing your friends and family, and if you are lucky, you find yourself and them a few days later still living.

Now, despite you lost your houses and your whole life changes from one day to the next, you also lost all your money. Everything, you put aside for later, maybe also for the future of your kids is gone. You have no chance to claim your private key or seed phrase. It's gone, unless you have shared the seed phrase with some trusted person in a different country / area.

How can technology help to fix this issue? How do you imagine this should be fixed in a BTC world?

All that self-custodial thinking is useless in such a scenario. And that's just one out of many scenarios, when people suddenly have to leave their homes, and have no chance to take their smartphone or hard-wallet with them, because you may lose important minutes or seconds to save the life of someone you love.

I am definitely not a pessimistic person, but these are real problems BTC will face when it comes to mass adoption.