You'll note that if its purely a numbers game, then Ironman could easily rotate the WC to venues which could support with 4000-5000 participants AND run a guaranteed to be sold out Kona as a regular IM at 2500 participants at the same time.

The better question though is - what does the funnel look like for people coming into the sport (new customers) and staying in the sport (repeat customers) under each scenario.

My opinion is that they should probably rotate it just in fairness and for the fact that most similar sports tend to rotate their world championships - but there are a lot of assumptions as far as how to grow the sport and where you put your WC.