I had never thought of such an idea before, but after reading about this, I think that it actually is a very good idea. We as a world could come together to build such a venue, and we could enjoy it for years and years to come. I say yes!
Personally I feel this makes sense. There is such corruption (reportedly) in the bidding process for events such as the Olympics and the World Cup. Having it in one city would cancel out this corruption, it would save on expensive buildings/stadiums being built and going into disrepair. It would mean that the economy of the chosen city and country would improve drastically and would improve peoples perception of the events. The fact that all the infrastructure, accommodation and facilities should be improved year by year will mean that the events can be accessed by more and more people, year on year.
However, does it make sense to have one main venue for the Olympics in one country, one main venue for the World cup in another country, and to have one of each on each continent so that the profits could be shared a bit more?
While I think that the idea of a central venue to hold all world sporting events is a well intentioned one, I think that the reality is that no one is really going to want to put the money forth to build and maintain such an endeavor, that's for sure.
One sporting venue should not be built to accommodate all of the world's sporting events. The purpose of many of these events especially the Olympics is to show case certain cities, as well as the cultures of these countries. If the events are held in one location all of the time this aspect would be taken away. Also, the events help stimulate certain countries' economies, so it would not be fair to have them in one country all of the time.