I don’t see how the median income doesn’t go down in San Diego over the next few years. Even if the rest of the nation doesn’t go into recession (unlikely), the downturn in RE-related income will decrease significantly thus driving down the median income.
Overall incomes can go up during recessions, even bad ones.
Consider that during the last prolonged recession in San Diego the median household income increased from about 32K in 1990 to about 37K in 1995.