DC's Iron Man From The Future
Iron Man and Booster Gold have, surprisingly, quite a bit in common, which one of the reasons Booster would have made a great candidate for launching a DC film franchise. Both superheroes use futuristic technology for superpowers, they both have AI's that assist them (Jarvis and Skeets), they're both egotistical showboats, and they both have strong redemption arcs. In short, they have enough in common to have made Booster a great "introductory" character to the DC film universe much like Tony Stark was for the MNCU.
But Booster Gold and Iron Man aren't identical! The pair are different enough that a Booster Gold movie wouldn't just be a clone of Iron Man. Sure, Iron Man might be a "textbook narcissist," but Booster literally founded a company to make money off his heroics, creating Goldstar Inc. to handle all the fame and commercial/movie deals he received after publicly saving the president. He is, by every definition, a commercially-inspired superhero.
This approach to superheroing, as well as other heroes' reactions to it, are what would set Booster Gold up for an amazing character arc of redemption and learning what it means to be a hero. Further, it's what makes Booster a naturally comedic character, one who is constantly showboating and being generally full of himself. Humor is what keeps MCU films light, fun and full of heart, and its something the DCEU could really benefit from more of. For all intents and purposes, Booster Gold is "DC's Iron Man of the future," both in his similarity to Tony Stark, and in how is character is the perfect setup for future DC films.
Setting Up The Future (Literally)
As a superhero who's from the future, Booster Gold's time traveler status could serve a greater purpose for the DCEU. We've already established that Booster would have made a great, low-stakes superhero to launch the DCEU franchise due to his similarities to Iron Man. However, there is something that Booster could have done for the DCEU that even Iron Man didn't accomplish: Setting up the future, literally.
Hailing from the future of the DC universe, Booster Gold's character is already perfect for planting the seeds of future movies. Even better, he worked in a museum of past superheroes! In a hypothetical Booster Gold movie, scenes of Michael working in the museum would be perfect for teasing future heroes' costumes, gadgets and villains. He even steals a Legion of Super-Heroes flight ring, laying the grounds for a possible LoS movie! His very concept as a character acts as the perfect starting point for branching out to other superhero films, something that not even the first Iron Man did.
Sure, Iron Man had Marvel Universe easter eggs (Cap's shield and the like), and the post-credits Nick Fury scene blew everyone's minds, but there were no hard signs that there were other heroes in the world. In fact, Iron Man was treated the first superhero to show up in the MCU, with little to no evidence that others were coming or had ever existed. Booster Gold's museum job and stolen tech are the perfect means to plant the seeds for multiple DCEU films, teasing future heroes instead of shoe-horning them like we saw with the video files Bruce Wayne stole in Batman V. Superman.
A Thriving Superhero Community
The MCU started with one hero, which led to others until, finally, they all came together in The Avengers. Since then, the MCU's cast of heroes has grown steadily as the universe has gotten bigger and bigger. DC could have put their own spin on the MCU formula, taking what had already been done and making it their own. When Booster Gold traveled to the present, he arrived in a time when heroes like Batman, Superman and pretty much every other famous DC hero had been at the superhero game for years, decades even.
Meaning, while there would have been room for build-up to more famous, "heavy-hitter" superhero movies, there'd be no need for some of the (sometimes messy) retconning that the MCU is forced to do. The DCEU would have already been thriving with superhero activity when Booster made his name. Booster chose the 21st century because it was the perfect era to become a famous superhero; the public was exposed to them everywhere. A Booster Gold movie would not only set up the future of superheroes in the DCEU, but also the present.
Plus, there's the possibility of sequels adapting Booster's team-ups with Blue Beetle and his work in preventing rogue time streams, both of which would make awesome movies.
What Could Have Been
Of course, at the end of the day, this is all hypothetical, speculation and "what-if." Regardless, it's kind of fun to think of how it could have gone a bit differently, possibly even better. Booster Gold, in both story and character, has a lot of the same elements that made fans love Iron Man. A Booster Gold film could even top Iron Man in how naturally the story sets up future heroes and films. To put it simply, Booster Gold could have been the DCEU's Iron Man.