It's something which seems crucial to me for reaching mass adoption (in addition to scalabilty of course...).
Already on this forum there is a shitload of people losing their Bitcoins by forgetting passphrases, the private keys, the dat file etc...
So I would like to know what technological solutions could be proposed for this problem.
To make a comparison, a lot of people are forgetting their credit card code (even if it's only 4 digits...) or losing the card and the centralized solution to this is the bank providing new card/code.
Which decentralized solutions to this problems could you think of?
Nothing, really.
The point of having a cryptocurrency in the first place is that you want to have full control over your funds. If there was a way to recover your funds then there will also be a way for others to exploit this method and hack your account. And this plus the irreversibility of bitcoin is a recipe for disaster as people will aim to hack as many accounts as possible in bitcoin instead of bank accounts because the transactions are so easily made.
If you can't store your private keys safely, then maybe you shouldn't be using bitcoin....