II'm afraid we'll be completely in the dark about the PS4 vs. XBO NPD battle in the coming years. May the best PR win.
Pretty much, we will see PR set pieces independent from NPD regarding sales, like the black friday Sony PR from last year iirc. Most likely there will be worldwide talk, shipped numbers etc. Especially from both Sony and MS for the next-gen consoles giving their products as much positive numbers fluff as poss..