This ruling, as I understand it, resolves a narrow technicality—but that technicality has potentially enormous implications.
The Court has only decided that the federal [EDIT: state! sorry!] government has no prosecutorial jurisdiction against citizens of the so-called "Five Civilized Tribes" in about half of OK—this is what the press means when it calls this territory "Indian reservations." They did not decide things like: Do the tribes get the taxes from people living in Tulsa? Do non-natives have to abide by rules of the respective nations? Does the tribal government have the ability to reclaim land through land-for-trust? And so on.
Further narrowing the ruling, my understanding is that this only applies when all persons involved in the crime (e.g., the victim) are also tribal citizens.
But, this ruling does open the door to a lot of those types of questions. It is possible we see several cases related to the sovereignty of these nations over the next few years, possibly greatly expanding the scope of the jurisdiction of the tribal governments.