Private keys and mass adoption

Dear all,

these thoughts came to my mind and I would like to share them with you to get answers. As we all know, the private key is what matters to access your funds (besides an internet connection). The problem I see for mass adoption, meaning real mass adoption where every John Doe uses it in his daily life, is the private key itself. In its current form, my guess is that professional custodians would take care of this as it is happening with many exchanges right infront of our eyes nowadays. In my view, this is of big concern: It is an easy entity to attack (compared to the case where literally everyone takes care of his or her private keys), were the attacker could also be the government. This reminds me a bit of the situation with the gold standard where gold was deposited leading to a situation of trust. As we all know, the paper certificates can be inflated as they are just claims which is a criminal act if the customers are not notified about it in my opinion. Nevertheless, this cannot happen in our case with crypto-custody, as we have a thing called the blockchain. So the dependency on the custodian and the risk of an attack remain which is still problematic if you think about the long run.

One might say, 'Well, just take care of your private keys by yourself!'; of course, you could and you can. But have a look at people you know and you probably realize that this is utopic and wishful thinking, we are even witnessing it just as I write this text that many people use custodians.

As I am not a cryptograph, I would be very happy if someone with deep knowledge could help me understand:

1) Wouldn't it be great if the private key were biometric? Meaning that with specific and independent body parts (eyes, finger prints and so on) you could access your funds, so the hashing function would be linked to your biometrics. Clearly a backup would be needed, that is why different and independent body parts are necessary as you might lose your hand or eye.

2) That being said, additional backups would be necessary in case you die and your heirs would own these funds. But how to achieve that?

3) One idea could also be that the setting stays as it is, but to access the private key you would need to enter biometrics. But the problem I see is that people can lose such devices; it is still better if your biology encodes the direct private key.

4) Has this topic (private keys in their current form and real mass adoption) sparked interest in the developer community? If so, what are proposed or discussed ideas?

I see that your biometrics change as you age, so it would need to be guaranteed that such bio-hashing would still work with the process of aging. Again, I am not an expert, these are just ideas.

Thanks!