It would be pretty unreasonable to change race time midseason to something else, especially longer, not all drivers have prepared to sit at least two hours non-stop, usually the full race lenght, first as an advisor and then as the driver or vice versa.
To me personally racing for 6 hours straight wouldn't be a problem if it didn't consume half of the day.
Just like Traxx said, maybe for next season, but not for the current one.