"the NX is meant to be 3x more powerful than the PS4. That sort of power only makes sense if it's a streaming platform."

You're confusing me. One minute you seem to be discussing streaming from the console, the next streaming to the console. They may coincidentally use the same English word but technically they have nothing to do with each other.

Streaming from the console may require a bit of extra oomph, but if you're designing it into the console from scratch you can add some custom hardware for it and it shouldn't increase general-purpose computing requirements. Streaming to the console by no stretch of the imagination requires anything to be 3x more powerful than the PS4; if you added 4K output to its graphics card, a XBox 360 would be plenty powerful enough to stream even 4K to the console. Sending video streams to the hardware decoder does not take a lot of power. Either way you don't need a lot more power for "streaming" either in or out.

As for specs, it will be coming out 3 years after the PS4 came out. The PS4/XBone generation is generally considered a bit underpowered compared to what PCs could already do at the time. CPUs haven't been advancing much but GPUs have still be clockin' along in the past 3 years. Being merely 3x more powerful than a PS4 is still Nintendo being conservative and not focusing on producing a graphics powerhouse, as has been their style for the Wii line, not some sort of impossible dream.