That's my thought to - haven't been able to think what on earth one would do with powdered peanut butter.
Just offhand, I would think it would be great for commercial production of peanut flavorings in candies, various baked products, ( like cookies ) and as an additive in cooking.
As far as long term storage goes, I would think that powdered peanut butter would last a great deal longer, never go rancid, and become a standard item in the kitchen spice rack, along with pumpkin pie spice, chili powder, curry, etc..
Add water?