There is a threat here, but it has nothing to do with the Unix copyrights. We have already established really, really well that the Unix copyrights are irrelevant at this late date. They can't be used like patents to enforce against other similar works. They were released under an unterminating BSD license and covered by a government standard. Forget them.
What they got was 481 patents that were part of a portfolio that Open Invention Network had previously used to defend Linux against patent suits. So, this is escalation in the patent war they are running against Linux, because they just removed one of our defensive weapons.