Question: Has there been any discussion about denoting the experts of certain topics, for example MVPs or Microsoft employees in the small profile icon? 

This way users can quickly distinguish between random internet morons like myself, and the ones accredited with their chosen speciality?

Answer: 
Why can't these users simply put this in their profile page?

These things shouldn't make a user absolutely trusted by anyone anyway. Voting should be done based on the quality of the post, not the user.
Reputation and badges are, roughly speaking, SO's way of marking people as possible experts. Certainly you can't put too much weight into someone's reputation without doing a little research into how they achieved their rep. But regardless, I cannot see SO doing anything to provide "external" approval of a person. If you want to make your credentials known, you can put them in your profile.