Would you be in favour of applying this policy to all people displaying behaviours deemed at higher risk of requiring hospital treatment? And who should decide what constitutes risky activity?

Not common and certainly changing in some ways but for example smoking had been deemed high risk. There are ways to model the risk here for at least some activities. Eg do you have a lot of speeding tickets? Car insurance goes up.

No, why would I pay more? In my country everyone pays the same health insurance contributions and gets the same standard of treatment.