@leocg It did existed in Opera once upon a time. I don't really know when it dissapeared, all I'm saying is that it's a questionable decision to let this capability out of the advanced options group, as it was before.
Look, I get this is a free software and I'm very happy with Opera, I think it's a fantastic browser, but not letting the user set their own file-type associations sounds a little bit absurd to me. And I'd like this decision to be reconsidered.
Besides, there's a problem in the way that opera handles certain file types or links, like magnet links... Is there any workarround, at least?