If you look at the historical sales of domains with Beijing in on dnsaleprice.com, it will underline that you are not going to sell any Rio 2016 Olympics domain names. There are just 11 sales of domains with the keyword Beijing in. The 3 biggest are Beijing.net twice ($50,000 and $18,100) and Beijing.tv ($9,100). The 4th biggest sale is just $2,625 BeijingStuff.com. Critically, none of the 11 sales has 2008 or the word Olympics in or anything to suggest a link to the Beijing 2008 Olympics.
The trend is even more exagerated for Rio De Janeiro, you have just the one keyword sale, RiodeJaneiro.info at $9,000 in 2004 and only a handful of very low sales for domains with just Rio in. Rio De Janeiro is a 3 word geo which is bad from a domaining angle and that would make pure Rio de Janeiro dot extension domains harder to sell. If short one word Beijing domains didn't sell in the run up to the 2008 Beijing Olympics, longer 3 word Rio domains definitely won't.
The underlying reason these domains don't sell is most people only want to what time the Olympics start on TV, if people are going to the Olympics, they will go to the sight they usually book their hotels and flights and book their trip, otherwise they will go to the big corporate hospitality company their company uses, the official Olympics site and so on. They are not going to type in Rio De Janeiro Olympics 2016 in Google, find Rio-DeJaneiro2016game.info on Page 57 of Google and spend $5,000 booking their trip 7 years in advance.
You can have 1m combinations of Rio De Janeiro Brazil Olympic Games 2016 Cheap Flights Hotels in 300 different extensions, none of them will sell, the only people who will benefit are domain registries and registrars. If you buy a lottery ticket, you have a very small chance of making alot of money, if you buy a Rio olympics domain you have a very small chance of making a little money. If lightning struck and you stumbled on a valuable Rio Olympics domain then it struck again and you got it on Page 1 of Google for Olympics 2016 searches, the Olympics organisation would come along and sue you so however you look at it, you can't win.