Ngspice has already been directly integrated into KiCad and will be available in the upcoming stable 5 release. I am not sure PySpice buys us anything we don't already have with Ngspice. We still do not have the schematic editor swigged out to python yet so using python in the schematic editor for simulation would have to be run externally which tends to be less than ideal for users.
Why ?
Question on Launchpad
ref. https://answers.launchpad.net/kicad/+question/658090
Wayne Stambaugh answer: