
Naturally, part of this smell comes from our own projected expectations -- something about opening the mint copy of a game you've searched years for is different than opening a new copy of Microsoft Office for Windows 7. Still, there is a tangible element of the smell created by the off-gassing of plastics, including chemicals like formaldehyde, phthalates, esters, and industry-made fragrances -- for example, the famous "new car smell" is actually a product of the glue they use to hold parts of the cabin together. Multiple studies have shown that these chemical cocktails are detrimental to your general health, but that doesn't stop us from enjoying the scent of Sharpies or heavily scented candles. These chemicals mixed with our expectations produce a unique unboxing for any given car, game, disc, or toy.
My thought: what if box-opening eventually becomes something similar to wine-tasting? If you look at it in the broad sense, there are plenty of parallels. To me, it seems to all stem from the concept outlined in this XKCD strip. Even if it doesn't pan out in the real world, it's definitely an interesting sci-fi premise to explore.