Instead of banning viewers who use other people’s login information, Netflix is attempting to embrace them -- for a small additional fee. Right now, two simultaneous streams per account are allowed for $7.99 a month. Netflix has announced a new pricing option that allows four concurrent video streams per account for $11.99 a month.
I read the whole story and I didn't see where it says that the concurrent streams have to be from the same IP. In fact, since they are trying to address password/login sharing I think they are specifically looking at multiple IPs per login credential.