CREATE TABLE table_name_78 (year INTEGER, regular_season VARCHAR, playoffs VARCHAR, open_cup VARCHAR)
What was the average year that the Nashville Metros did not qualify for the Playoffs, did not qualify for the Open Cup, and had the Regular Season 7th, Southeast?
SELECT AVG(year) FROM table_name_78 WHERE playoffs = "did not qualify" AND open_cup = "did not qualify" AND regular_season = "7th, southeast"