I can't see that happening for a VERY long time since the Olympics champion the pinnacles of human physical achievement. The only events not directly/solely related to human performance are the equestrian events. In my mind, the view taken is too narrow as it seems blatantly obvious to me that there should be several dog-sled races (sprints and marathons) in the olympics.
Now, to get to where we have robot fighting in the olympics, the following would have to occur:
1) Robot fighting becomes popular, with formal leagues, clear rules, and a large fan base
2) The system evolves so there's a clear hierarchy of 'the best' in different categories
3) Some human fighting events go 'out of vogue' -- for instance boxing, UFC, martial arts, etc are deemed too dangerous or 'too aggressive' to be countenanced by the games.
4) More events not primarily based on human physical prowess enter the olympics -- dog-sledding, etc.
5) Olympic rules for some events change to allow more 'physical assistance' -- that is you get runners with special 'blade legs', swimmers with physically implanted 'fins', etc.
So, if all these occur (preferably around the same time), you could have a situation where there's an opening to include robot fighting