As much as this is interesting, I don't see how it's supposed to be applied to any video game efficiently and I rather read the "normal way".
On a general point of view :
For people who aren't used to read fast they may read faster, but that's about it (that's the point of the thing anyway).
But for anything lengthy, you will still have to check the backlog/real text on a regular basis as you're not a machine and can't keep up with the same speed in the long term (be it slow or fast). Even if you have no trouble to understand at 600 wpm, you're bound to lose attention sometimes and with this system, every second of attention count.
Surprisingly, it's perfectly understandable in a foreign language.
Good app for reading news, comments & boards if it doesn't bother you to change your way of reading.
On a gaming point of view :
Aside the constant backlog-check issue, focusing the eye on a single part of the screen too much isn't the best choice of game design, even for a visual novel.