The answer is unpleasent.
Someone (with massive resources) already tried it in 2011 and was burned by the market. Kyocera hit the wall with Echo concept because android was not easy to adapt to second screen and it brought near zero advantage because few software ever supported it...
Only the homescreen and video playback was merged to one picture and you could place apps on either screen but not overlap afair from seeing the device around 2012.



The few apps they made working on both screens only made it obvious that the spacing between the screens was the main showstopper back then.