When you sit down to watch a film that features a diabolical supervillain, that villain often has some truly amazing gear with which to irritate the good guys. While the hero still wins out in the end, the gear that a villain carries could, with a bit of repurposing, be made quite useful to society.
The idea behind diegetic prototypes speaks to what these devices could do if they were used for good. If you sit down to watch the movie a few more times, you may come to see how the gear used by the villain could be beneficial to society. However, you must have a clear vision for these products and how their purpose has been turned from evil to good. Let’s face it, no one is going to finance your projects if they think you are just some crazed nerd who wants to make a red light saber.
When your inventor gene gets inspired by things you see in movies, you do not necessarily need to stick to the things the good guys use. Sometimes, the weapons that the villains use could be put to good use in the real world. You could create better body armor for police officers, better defensive weapons for private citizens or medical items that could save lives. Your designs will be on the cutting edge of design, and they will stay there because your inspiration is far higher than the inspiration behind most products.
Just imagine the possibilities that Dr. Victor Fries‘ (Dr. Freeze) ice ray could present to the medical industry. Not to mention Dr. Otto Gunther Octavius (Dr. Octopus or Doc Ock), who had a mechanical exoskeleton that bears a remarkable resemblance to some real-world devices now being developed to help the disabled walk and to help factory workers deal with heavy lifts.
When you have fully formed the idea behind your prototype, you can explain to people how something that was once used for evil can now be used for good. This transformation is beneficial to everyone who uses the product, and it makes for a good story behind the product.