There is an Xposed module on these forums somewhere, that enables immersive mode everywhere. It has a few flaws though, as some apps just don't work right with it, or once the navigation bar pops back up, it cuts off the portion of the screen.
However the ones that did work with it, it worker great. It would be nice for someone to make an app or tweak to force selected apps into immersive mode, while allowing the navigation bar to stay where needed.
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