GM might launch IPO of company stock later this year, but conditions have to be right
Economy, financial markets, and vehicle sales have to improve, and GM must be profitable before that happens
Liddell noted that GM operations in Brazil and China are profitable, but Europe remains "challenging"
North America is somewhere in the middle, he said
Viewed by many as CEO-in-waiting, Liddell was Whitacre's first major hire
Liddell says it's too early to speculate if he'll succeed Whitacre