So, my experience may be part of the reason the market is not there. In my way-back machine, I had one of the original "Pocket Pc's", a HTC 8525. I liked the device (it was really more of a tiny computer than phone) with the slide out keyboard, and integrated well with Office.
When I finally laid it to rest (sadly), the one issue I had was that my eyes no longer could cope with the screen size (I tended to use it to type full emails, not just quick texts) and some spreadsheet work. In any case, at the phone store, I asked;
"What's your biggest device?"
And was handed the original Galaxy Note (which I just replaced with a Note 4).
Through this period, tablets were theoretically the "hot item" (as well as all the electronic book thingies).
Never saw the purpose. With the Note, I could pretty much do what the folks carrying both the phone, and tablet around could do. And it was a phone.
The marketing gurus, I believe, missed the impact of the larger devices (really can't call them phones, and phablets is too goofy). For what people use a tablet for the Galaxy (and the iPhone 6+) handle. If I need computing power, either a desktop or laptop, but not a tablet.