Netflix for XBMC has been an ongoing issue as well as other paid streaming services such as Amazon Prime for XBMC and HBO Go for XBMC. Hopefully, this will give you a little insight as to why it is such an issue and the best way to resolve the problem.
A Little Background
XBMC is an open source software with very little limitations to media playback or addon capability. On the other end of the spectrum Netflix, Amazon Prime, HBO Go and many others have strict requirements to prevent piracy. Given that XBMC is open source and these streaming have strict requirements, it makes it almost impossible to have these services available to playback within XBMC.
Building an XBMC for Netflix Addon
This has been an ongoing problem. Netflix for XBMC addon has been attempted many times. Givin a usually complicated install, it was working at some points. It is now once again dropped due to the complications and restrictions with Netflix itself. This is mostly true with other services such as Amazon for XBMC and HBO Go for XBMC. Though they have been attempted, they have all eventually failed or never came to fruition.
How to get Netflix on XBMC ; Solution
Currently, the best solutions for playing Netflix on XBMC is to buy an inexpensive, well supported box solely for paid service playback. Apple TV (Non Jailbroken) & Roku are among the top supported boxes for paid services and relatively inexpensive. You can more or less get Netflix on XBMC for about $150. A Roku box, that is well supported, will run about $50 for the low end model, which is all you need. A Taffy Media Center, XBMC Only Box, will run about $100. This is the best and most reliable way to have everything working properly all the time.