Now that LAX - HK and HK - LAX flights have Premium Economy, your chance of getting bumped up from economy to Business is even less likely. Most likely if economy is oversold, they will bump passengers from PE to Business and Replace the PE seats with Economy passengers.
I got bumped up from Thai PE to Business several times when Economy was oversold (This was when Thai still had PE from LAX to BKK).
I'll be trying CP's new Premium Economy in Feb.