The Centrium will be invaded by the Diamond Authority if the series reaches the point of having an Intercontinuity Crossover with another CN property.
Either to acquire the mysterious teleporting jewel Frankie discovered or as a step in a bigger strategy to conquer and destroy more planets via colonization. Potentially as a temporarily/mildly Darker and Edgier multi-part story where the radically diverse alien inhabitants of the Centrium have to work together to defeat Homeworld Gems that fully embrace the Scary Dogmatic Aliens status that their home series glossed over. The Amazing World Of Gumball and Elliott From Earth are Mutually Fictional
Both are cartoons within the others universe. Also on opposite ends of the Animated World Hypotheses as while Gumball's characters are obviously toons, I can't imagine Elliott being anything other than "live-action in-universe".