Well Viva...you may get more than you bargained for with your question.
This "folly" has been around for years and is about as likely to happen as El Al serving Baghdad.
El Toro Marine base was shut down during the base closing spree of the late 80s and there has been much talk around creating a new international airport to replace SNA and its capacity constraints. The problems, and there are many, lie primarily with surrounding residential communities, environmental impacts, and co$t$.
As a native of Orange County, I think it would be great to have a "world class", but my cynical side doesn't ever see it happening.
But I'm sure there will be others who disagree!