They're assuming 4 connected devices for every human on the planet in 2020. I'm guessing the lower half won't be able to afford any at all, they're lucky to eat and drink clean water and maybe have sanitation facilities sometimes, which boosts the sales load to maybe twenty for every upper middle class American, per year. However by a pigeon-hole principle its going to be difficult to wear more than one pair of shoes at a time, and my generation hasn't worn a wristwatch since the 90s, and probably isn't going to start again any time soon.
Its interesting tech, but exponential charts going into the indefinite future make it look more anti-propaganda by an opponent more than someone into it. For example if the smartphone growth curve of 2007 continued into today, I'd have to carry 850 cellphones in my pockets this year, and 2025 phones in my pocket next year, or whatever. Things that can't continue forever tend to stop after awhile.
As an early adopter type guy I find my fitbit to be completely useless, no actionable items or decision making is actually done (as opposed to "people should" type of talk). On the other hand, the scale I bought from the same place gets used every day and its nice and slow and clunky at taking measurements (intentionally?) so consciously or not it provides some actionable data / motivation. Although it varies in the short term by 2 to 3 pounds, I've lost about a pound per week since buying the scale over a long term because I don't like seeing the numbers go up consistently.
The problem with "smart underwear" or whatever wearable product is not so much to convince people that "people should care" in an abstract sense but get them as individuals to actually do something. In that way its an aspirational good like paper encyclopedias used to be, which were mostly sold to illiterate people who never read them. "People should care" about how many steps they take in a day. I'm a serious hiker/walker type and even for me my fitbit is much more a discipline tracker of how often I forget to wear it than anything else. The proper market to compare them to is the paper encyclopedia market, not the cellphone or social media market.
The other problem in the field is product fluff. Yes a magic star trek tricoder that sends my real time EKG to a doctor would be really cool, but all the industry is going to provide is a sorta inaccurate pedometer and you'll like it. Or more likely, not, and when the buzz dies down and the industry segment shuts down you won't even get that anymore, which is too bad.
The main thing my fitbit does is get triggered into sleep mode in my pocket, which annoys me. On the other hand taking it out of sleep mode is often my only interaction with it.
