Imagine an UI with a circle and the spritz box above. You put your thumb in the middle, push right it starts to show the words forward, push farther from midle => faster. Push it left => slower. Left after middle, rewinding text.

You could even use up, down to go back entiry frases or paragraphs.

Regarding linearity, you could use color/color fading to wrap phrases, or show two to four words per time moving just the red letter according to speed.

Personally... I think it's an amazing Idea! :)