I think this niche doesn't get filled because of the gap between what you want and what you buy. The gap between what you (ought to) want and that which makes a good first impression on you.
I have, use and like a small android phone called "unihertz jelly pro", small enough to fit in any pocket and good for my use. After a while with that phone, using a phablet one evening was an absolute eureka moment. I was looking for some sort of product, and on the phablet all the photos looked good. Inviting. Desirable. The whole phablet was fun in a way the small phone wasn't.
After that experience, I can understand that people reach for the big phones in the shop, even if some of them may really want something different in the long term.
And I can understand why retailers stock the phones they do. The phone where instagram looks good is the phone with the right first impression, and one has to optimise for getting the goods out the door.
(http://rant.gulbrandsen.priv.no/unihertz has blah about how I tweaked the phone, if anyone cares.)