[Someone]

I think part of the thinking behind this is just scientific curiosity (“let’s see if we can do it”)

They collect the wastewater kilometers from the sporting events, so spatial and temporal resolution (where was this dumped into the sewer? When?) will be too low to target individual users.

Application I think will at best be for policy development (what sport should the doping agency focus on? What chemicals? Do people use that new thing that’s being talked about?), not for catching individual users, and probably not even for use at the event being monitored.