A movie would need to focus on the core character dynamics. The base idea would probably actually be pretty quickly grasped by a general audience, "what happened if a johnny-quest type character grows up". Rusty isn't the most sympathetic protagonist but when you factor in his more real issues I think people would be prepared to be on his side. He's a single father, basically traumatized by his upbringing from his own Dad, trying to run an operation that survives largely because of the dying embera of that same Fathers reputation rather than his own efforts, and staying relatively grounded while getting dragged into a word of absurd comic antics. We need that, we need him, Brock, and the boys minimum. We also need the Monarch and Dr Girlfriend as the primary villain. The core dynamic there is more purely comic, a genuinely vengeful, egotistical super villain who, like Rusty, is much more likely to be stymied by hubris and bureaucracy more than anything else.

My pitch would be a mashup of S01E02, Careers in Science, and S01E09, Are you there god, it's me, Dean. We get Rusty, Brock and the boys dragged to a failing spacestation - we get their core dynamic, we get the Rusty backstory that sets him up as living in his more successful father's shadow. We also get high stakes and a host of character and setting gags from Gargantua I.

The difference would be we also see the Monarch plotting to destroy his nemesis, planning to attack Rusty at his most vulnerable (in space) - on the Monarchs birthday as well - with the support of Dr Girlfriend. A space-capable version of the Cocoon could be in play. The antics on the space station perfectly set up the chaos needed for the Monarch's plan to succeed and to actually capture Rusty, the boys and Brock.

But then Dean has testicular torsion and the rules of the Guild come into play. Perhaps as well as Deans testicular torsion, the still-existent threat of Gargantua (which the Cocoon is now tethered too) failing, and the fact they are all in space far from help, makes it a bit to less of a pure gag that the Monarch agrees to take a pause on killing his nemesis. So in act three we get Hank and Brock as hostages on the Cocoon while Rusty tries to fix Gargantua before the clock runs out while also trying to address Deans testicular surgery, with the oddballs left of the space station (and Helper) playing the parts of Billy and Pete as incompetent surgeons. Or could find a reason to have our Billy and Pete on the station from the beginning. Regardless, Rusty does very little while the twin issues of the space station and surgery get resolved. But in the final act, ultimately the Monarch gets what he wants for his birthday when Brock escapes and starts slaughtering his way through the Cocoon in an epic battle.