I think this is at least partially a feedback loop issue. There aren't manufacturers even making small screens, and the time/cost of doing that isn't seen as worth investing in... because... look at what's selling - larger screens! - which are the only thing we're selling because... look at what's selling!
A small niche player that wants to try a different form factor/size isn't practically able to enter the market with anything but commodity screens.
I'm not sure why you're asking me, but the OP's site says that 5% of iPhone orders (10 million phones a year) are the mini. That's quite a large market in absolute terms.
99/1?
90/10?
80/20?
I don’t know this myself. But I figure that if no one is stepping into this market, it’s probably pretty damn small.