All they need to do is form a group again.
It's just going to feel repetitive. You can't top the 1st MCU plan that lasted 3 movies every year for over a decade.
You might get one more good movie out of an established group -- like FF and mostly because it has an epic villain built in -- but Gunn pretty much burnt through the "surrogate family of oddballs" formula.
At this point, the odd pairings -- like Wolverine and Deadpool -- buddy-buddy nonsense might be the way to go.