There are a number of valuable use cases that are missing not technology but a schelling point.

If there were a meta platform that everyone was willing to trust nearly completely to upload their data to, then a number of simple use cases become viable with only a little effort.

Especially if everyone knows that everyone knows that.

The meta-platform's killer use case would be the alternate laws of physics of AI.

The assistive possibility is a secondary use case.

The reason they're killer is because everyone wants them but it's not possible to do in the current laws of physics.