Actually, I bet you're pretty close

Hi,

My two guesses were the improved battery and a personal transportation device.

The article says Bezos gave his trademark "loud, honking laugh" when he saw it, which he probably wouldn't do over a battery. Also, the names Metro and Pro sound like a PTD. Also, Kamen already invented a wheelchair that climbs stairs.

Also, previewing this for Jobs and Bezos shows that he's looking for a kind of "free-thinker" support, which a PTD will need. As does the tactic of writing a book about it. In other words, Kamen is trying to avoid the fate of Preston Tucker.

Best,

-Boyd