Hi there
Most likely there will be a successor to these cameras, but whether it will be just one model or two, and when (given the declining digital camera market), remains to be seen.
I will say, the KP's image quality and high ISO performance is among best in class at this point in time, and the K-70 is very nearly as good. I wonder, are you using all the techniques available to you for low light shooting - e.g. fast lenses, tripod, off camera lighting, shooting raw and using post-processing noise reduction effectively etc.?
We're reaching the limits of what current sensor technology is capable of. Indeed, cameras like the K-70 and KP (even the full frame flagship K-1II) already use hardware modules to process noise generated by the sensor at higher ISO settings. So whilst it's possible we might see small incremental improvements in high ISO performance from replacement models, I wouldn't expect those improvements to be game-changing...