A recent KPBS discussion on this issue, mentioned that joint military/civilian airports exist in some other cities. I assume it is viable, because the Airport Commission made a short list of viable sites. The only obstacle to the Miramar site is the government’s insistence that they don’t want to be bothered with it.
But why does San Diego need a bigger airport? With all these people moving out and the fiscal problems, plans for a bigger airport and bigger port should be shelved for 20-30 years.