The feature sparked security concerns but apparently it was so little used that Microsoft decided to remove it from the latest Windows 10 build as the low userbase didn't justify further investment:
There were security concerns related to Windows 10’s management of passwords and whether or not said passwords could be intercepted on the fly. To our knowledge, no security breaches or problems were associated with Wi-Fi Sense. According to Microsoft, few people actually used the feature and some were actively turning it off. “The cost of updating the code to keep this feature working combined with low usage and low demand made this not worth further investment,” said Gabe Aul, Microsoft’s Windows Insider czar.