Work is an issue. I've heard of teenagers leaving school to start unschooling. Even at that age it is beneficial. In that case it's not uncommon for those kids to spend a good year doing nothing but playing video games until they get bored and decide to pursue other interests. That could be a daunting year.

But my point is, if it's not an option when the kids are young due to simply having to work (I realise you can make every sacrifice to be sahm but sometimes that's just impossible due to debts or whatever) then you can introduce unschooling at an age when your children are old enough to entertain their own interests.