Huh? Worgen were running around in silverpine forest for a long time, there is no indication that dk's are required to be inhabitants of the plague lands. If that were the case then only humans and forsaken and blood elves should be death knights, along with a few dwarves maybe, because these are the only races that live in and around the plaque lands. Even in Wrath itself the LK recruited everything he deemed somewhat interesting and turned it into whatever he wants, be it deathknights or some other kind of abomination. Goblins are all over the place too, so them becoming deathknights begs the question why the LK deemed them worthy .
Ogres surely could be DK's, Naga though is a bit of stretch, because they are very dangerous foes themself and their presence within the scourge definetly needs a retcon.
All in all the racial restrictions are one of the few things blizzard has done well as far as I'm concerned. They still haven't allowed tauren rogues and the worst thing so far were some of the MoP constellations, which make sense considering the races have intermingled for quite some time and there is no reason to reject a tauren that wants to be a servant of the light. They also said no to panda dk's - thank god.