I would like to see a folding Kindle from Amazon. This is so obviously possible with the current width of a Paperwhite, which is even not the thinnest available, that we could have a folding Kindle able to display two full sized pages (like a real book) or one page with a seamless single down the centre to create a pocketable eReader to carry anywhere. Hurry up Amazon!
Garmin needs to add true mobile connectivity to their higher end products. Simple as that, the top-end Garmin watches are superb and 4G would open up podcasts, music etc for a truly impressive device that could finally compete with, and beat, the Apple Watch.
Before Apple even considers a folding iPhone, how about a folding iPad? This appears to be within reach technically and would offer a huge number of benefits.
Apple also needs to sort the Apple Watch battery. A power strap accessory? That would make sense to me and if they can do it better than the pretty lame third party efforts so far it could change everything.
I was going to mention a 4G MacBook, but in reality that is not needed with personal hotspots and so much Wi-Fi around. Anything else I am missing? Feel free to get in touch.