I read through the 35-page thread about this on websleuths.com last night (just to torture myself, apparently), and some of the highlights were someone asking "for someone who can check, did UHC stock go up or down today?" and another person asking if they had ruled out the sons yet, since they are young and white. The kicker is they all think they are clever detectives when most of them show zero ability to use Google or read any posts/updates made before their comment. I don't expect any Reddit threads to be much better.
I wouldn't be surprised if the killer was trying to target any of the UHG suits, because if he was really keeping close tabs specifically on Brian Thompson, he wouldn't have been casually getting food and water at the Starbucks down the street and get back to the hotel only 5 minutes before Thompson walked by. I'm sure if it were Andrew Witty who went by at that time, he would've been the target.