important things are often boring -- and there's almost nothing you can do about it.

That's downright ridiculous. The most important skill for a teacher is an ability to effectively impart knowledge and in order to make students listen and remember, you need to make them interested.

So they need to make everything else less interesting.

No, they ABSOLUTELY don't. If I'm watching a fascinating TED Talk at home, I don't need anyone to make my favourite tv show boring in order for me to pay attention. That's not how attention works. For someone who seems at least dimly aware of the existence of dopamine, you seem remarkably confused about the effects of a lack of it.

If there are kids for whom this is a difficult situation and they're unable to cope, such kids will need intervention. I.e. restrictions in free time as well.

So restrictions are your only tools? I really hope you're not a teacher or a parent, because your ideas seem not just ineffective but actually borderline abusive.