Seems to be adding two specific items to the existing Act, one a definition, the other an ammendment. The added definition:
"Native American" means cultural items that have a significant and substantial genetic or cultural relationship, based on factors other than geography alone, to a presently existing tribe, people, or culture that is now indigenous to the United States.
and the amendment:
Nothing in this Act shall be deemed to restrict excavation, examination, investigation, or scientific study under the ARPA Act of 1979 of any cultural item found on Federal land that has not been determined to be the property of an Indian tribe or a Native Hawaiian organization.
The new definition is directly aimed at recent attempts to broaden the definition of "Native American" to any non-European remains regardless of whether or not they have a direct relation to existing tribes.
There is an extensive article on NAGPRA in the latest American Antiquity which no doubt has much bearing on whether this legislation is needed or not; I read it a couple of weeks ago and was going to post on it, but haven't gotten around to it yet. My first impression (see here) is that the new definition codifies the court rulings that specify that NAGPRA doesn't even come into play (though ARPA does) with remains of a certain age. This is what the famous "or was" bill was all about. That is, NAGPRA needs remains to be "Native American" to even apply, and this bill restricts that definition to remains that can be directly linked to existing tribes through something other than simple geographic proximity.
The second part looks to prevent the rounds of lawsuits regarding these sorts of remains. That is, if it's not under NAGPRA (i.e., not "Native American" in the above definition) it's under ARPA and suits claiming NAGPRA jurisdiction are automatically off the table.
Must go re-read that article. More will no doubt follow.