I got to know Cao briefly when I ran the largest fansite for an MMO he helmed, DC Universe Online.
I remember that game having to be retooled partway through development because Cao read an article that a human being couldn't handle more than 8 options at a time, so he demanded the game's power system be changed so players can only use 8 abilities at a time (rather than a full MMO hotbar), causing a rather late game rebalance and redesign. It seems he may have taken that style of production to Sigil.