There seems to be some consistency in the rumours but we don't have the full picture. I'd be surprised if a tablet wasn't involved and the tablet doesn't have removable controllers. Also I think the performance box is and indicator of VR. I just can't see a portable system having a performance box but I can see a VR helmet/visor with slot in tablet needing a box for more computing power. I.e. for home and VR use the performance box is used but for portability just the tablet on its own.
If Foxconn are already testing manufacturing then I can only assume Nintendo are very happy with the gaming experience the NX is capable of and want to time release details for the maximum impact that will last until launch. Alternatively the launch is delayed perhaps they are holding out for AMD Zen architecture.
