Migration for certain prominent projects is already underway, e.g Ethereum.

It's too late.

How are you going to mass migrate all of the cold, dark wallets?

It's not going to happen because it requires conscious, deliberate, careful migration on the part of the wallet owners. You won't even be able to contact or warn most of them, let alone get them to understand the process.

Probably half the value in Ethereum and Bitcoin will be popped this way.