I definitely think there is a missing link...
First, SnapDragon SoCs are so far past any handheld ever released in the past, and smartphones are so ubiquitous, handheld makers are completely ignoring existing platforms with obvious gaps (A Steam-like or Origin-like system with real backing, exclusive developments, access on other platforms)
The biggest thing is of course physical. When Samsung and Oculus can sell >5 million VR headsets for $99, why can't we get a slim, pocketable controller that grips on the sides like the Steelseries? Maybe add some premium features like sensors, bluetooth, speakers w/ headphones, battery bank (Since it'll likely cover those ports), maybe even e-ink buttons with colored LEDs, NFC and external peripherals.
Make it work with all Android phones with a certain minimum chipset, and introduce some kind of best-fit settings for phone resolutions and SoC combinations.
At least I can see a market for it. It would take a Sony or Nintendo to do this, though.