The Olympic marathon should be an open race allowing as many people as the roads can handle. It should have a reasonable entry fee, with the proceeds going towards scholarships for those around the world who actively promote the running community but cannot afford to travel to the games. Only the top 3 receive medals, but each and every participant should be able to call themselves an Olympian.
The Olympics is supposed to be an inclusive event where people from around the world come together. It is a competition, but it is NOT an elitist and exclusive one. It is also NOT in the Olympic spirit to exploit the citizenship laws through your connections and then brag about being an Olympian to sell movies.
Now, for most sports, you have practical limits, because there's only 8 lanes on the track and only time for so many beach volleyball games. However we know you can have 50,000 people in a marathon and with the right planning and logistics I believe we could increase that to 100,000 or 200,000.