change focus between two views in split view
I'm going to post a different question to see if there's a way to write an applescript/keyboard maestro macro to hack this together using system properties (since I'm sure OS X is storing somewhere variables that encode which apps are splitting which space, what the current space is, and what the current focus is). But this answer to the question Switch focus in split view makes it seem like there is no way to do this by default either across 2 different apps or within two instances of the same app.

In it they suggest using ⌘` for moving between two instances of the same app, and the closest by default would be ⌘⇥ for different apps.