Norway may implement that in a sensible way, but the UK recently scrapped a similar sentence because it was linked to a bunch of injustices.
https://en.wikipedia.org/wiki/Imprisonment_for_public_protec...
People would go in for a minor offence, but be seen as high risk, and then stay in for many years.
Every 5 years after the main sentence the person is reviewed to see if releasing him would be a risk to society. And if deemed such a risk, the sentence is extended by another 5 years.