The 2013 Dota 2 "International" tournament had a very non-regular tournament when it got past pool play.
The easiest way to see it is at this link about two thirds down the page. http://wiki.teamliquid.net/dota2/The_International/2013
The best way to describe it is a double elimination tournament with play in games to the losers bracket.
Is there anything in the works for customized tournaments like this?