I have heard that according to the latest technological advancements, there is a possibility that 128 bit OS will be launched soon. Is it true?
Yes. 128-bit CPUs and OSes are surely just around the corner. Mobile devices too. In fact, I'd suggest not buying any new hardware for now. Current 64-bit hardware will be completely obsolete when the 128-bit revolution hits, fit only for the scrap heap.
Of course, there are those who argue that even 128-bit technology is just a stepping stone on the road to quantum computing. Within a quantum computer, each bit (known as a Qubit) operates in multiple dimensions making them exponentially more powerful, and making comparisons with traditional computing technology meaningless.
Personally, I wouldn't buy the iPhone 6. Wait for the first Quantum iPhone, it'll be worth it!!