Do you have a proove for that
well, one cant be 100% sure. however its based on what we see today in the market and what nintendo logically can do.
WiiU uses PowerPC architecture, which is something rarely seen in the market nodays. PS4 and XB1 use X86 architecture. which is seem in pretty much all PC's. AMD, Nvidia and Intel proccessors and GPU's. Nintendo could make a more powerfull machine, with a cheaper price and easier to develop for using X86 architecture, not PowerPC. so its most likely they will go with an X86 architecture for the NX.
what that means is that it will be VERY hard for NX to have backwards compatibility. because they dont use similar chips and architecture. however, never say never, the 360 is PowerPC based and XB1 is X86. but the backwards compatibility is through emulation, not real BC. and its much harder and time consuming to do.