When he wrote 'arpeggiator', I was thinking this was going to go in another direction- holding down a single key that starts at a letter and then releasing the key as it reaches the letter you want. Because when I think an arpeggiator on a synthesizer, it's done via holding a key while notes repeat.

I always was very good at texting on a number-pad phone, via repeated presses- pressing (4) two times for a "H", pressing (3) two times for an "E", pressing (5) three times for an "L", etc etc. I was so used to this that I didn't even progress to using T9 texting before blackberrys and smartphones took over.

So I thought... taking that idea, and doing a press-and-hold while letters scroll by, could be pretty fast. And you could dial up the repeat rate until you started making mistakes. Map 8 keys for letters, one key for a space bar and long-press for extras, one key for backspace and long press for extras, and I think you'd be able to hit much more than 10 w.p.m. that the author winds up hitting.

Only problem: this can't be instantiated as a normal USB compliant keyboard and allow you to see the letters scrolling as you hold, without a specialty keyboard app for the phone.