My proposal for the mixed event for the Olympic Games:
It would be a 1m/1w team, during 3 days of competition and woukd race a total of 50km. Multiple day events are common in RaceWalking, with a event in China hosted yearly being super popular. The four first events would work as qualification for the last event, a modern-penthatlon style.
First day: men's and women's 35km race walk. Different qualification for sex. First place gets 0 penality seconds, 2nd gets 20, 3rd gets 45... and so on.
Second day: rest day
Thrid day: 5km time trial. Different sex qualification. Same puntuation as the first event.
Fourth day: 2x2x5km rellay. Here is where the total penalty seconds "won" in the 4 prior events get added. The relay starts in the order of the time penalty, just like in modern pentathlon. Every 5k theres a racer change. First athlete to cross the finish line, wins, and so on.
Something like this would have 50km raced by every athlete, a 4 day event, a mixed event, different types of races and a "chase" style finale already proven a hit in modern pentathlon or the EuropeanGames DNA event.