The answers are not necessarily the same for all those, and for all future scenarios. The conventional answer today is that sport should promote, among other things, a healthy life. Taking large amounts of amphetamines is not so healthy, but some of the currently-legal ways that pro athletes prep for competition are also not very healthy, like the use of extreme and possibly dangerous amounts of caffeine in many sports. Maybe people will do more bike touring than bike racing because racing has become pointless and un-compelling to follow as a fan.

It may be that many professional and elite amateur sports will not survive genetic modification, for example, because anyone can access elite athletic potential if they wanted to. Or, more disturbingly, only if their parents had chosen a genetic combination for one outcome over another. What would be the point of "being a fan" of an athlete with characteristics chosen from a menu?