> I don't think ads will be built into the main replies, 
  > because people will quickly lose trust in the results. 

The 'best' ads will be those the public doesn't recognize. Surf the internet without an ad blocker and you will die from a heart attack. This is a matter of conditioning users. It will take some time. Case in point: people already give up on privacy because "Google knows about everything already", which reflects a normalization of abuse, as we started from trust and norms ("don't be evil").

So, can they? yes. Will they? yes.