Consider the iPad. Isaacson's book revealed that iPad prototypes and multi-touch was actually created years ahead of the iPhone. However the power/weigh/performance ratios just weren't there for a compelling product. It was not until the scale of the iPhone drove down costs and improved technology that a compelling tablet experience was possible that Apple released the iPad. And even then in 2010 this was not an easy task. Go back and read the reviews for all the "me too" Android tablets that launch in the 2010-2011 compared to the original iPad. This is just one of a number of examples.
Apple will release a new product category if and when it feels it can make an impact there, not because of a time table set by technology pundits or analysts. This is just how they work.
The only viable one I can think of is wearable tech, and definitely not a damn watch. I think Apple won't cater to as niche a market as wearable medical, and let 3rd party use their hardware to attack that market space.
The two biggest for me will be an App Store for the AppleTV. This could put the end to Nintendo's console hopes forever and open up a lot of new revenue streams. And the biggest by far is payments. iBeacons is starting to take off and with AppleID/TouchID they have the frictionless security mechanism.
Surely there is untapped potential in giving people greater day to day insights into their health, and obviously a lot of people care about their health.
Until it can analyze sweat for illnesses and nutrition info that won't get Apple in trouble legally (FDA...) and will spare you from going in for a check-up, then I don't think it's feasible at all for them to venture in that area.
MP3 players, smartphones, and tablets were all small "niche" markets before Apple entered them.
Look at how long it took Apple to do a tablet. The iPad launched more than a decade after Microsoft pushed their tablet vision; heck you could buy iBook tablet conversions for years before the iPad.
Samsung rushed their watch out the door to beat Apple to the market. Result: total dud. I'm not eager for Apple to try te same thing. Tim Cook will achieve the best success by pushing his folks to NOT launch until they have a blow-your-mind level product.
2) They have gone on record saying that they will introduce "new product categories" this year, so we'll see whether they keep their promise.