According to Shaun Himmerick, the executive producer on Mortal Kombat X, the latest title in the franchise won't require Xbox Live or PlayStation Plus to play your friends online. In a twitter exchange, Himmerick responded:
@berserkerlbs ps plus is not needed for any feature of MKX.
— lover of tacos (@lover_of_tacos) February 22, 2015
He later clarified this extended to Xbox Live too.
Honestly, I don't see how this could be true. I severely doubt Microsoft or Sony would allow this unless NetherRealm is footing the bill for server costs on their game. I very much doubt that too.
I suspect there is something lost in translation here, but who knows. Maybe it is true. In which case, that would be an amazing precedent to set.
Thanks to LazyGamer for the heads up.