Well, this sounds like a custodian solution. It destroys the main advantage of nostr - absence of centralised places controlling our profiles. If all the private keys were stored in one "storage", then the government will go to that place (like it goes to facebooks and twitters) and install censorship there.

Also, normies don't use many clients. Install Amethyst and use it. Why to install many clients? If you are a geek kind of user, who is curious about software, I understand that. But it is not a big deal for such kind of users to copy-paste nsec from one app to another.