The problem with the old policy was that the Park was taking the responsibility unto itself by saying that a 7 year old would be safe alone. Of course that all depends on the 7 year old. So now its up to the parents - the way it should be. This does not affect me personally because I don't accompany my son on rides just because a sign tells me to. I do it because that is what I believe I should do as a responsible parent.
Some people are absolutely unbelievable.
So yes, with this new policy, it is up to the parents, there is no rule or regulation against young children riding alone. Yes, young children can go on rides alone according to this new signage. In my opinion, there are two groups who will suffer most for this policy, the first is the children who are cursed with irresponsible parents. There are far too many children whose parents would and do let them ride unsupervised. I know that if I were a CM, I would tell young children that they should go get an adult to ride the attraction.