Realistic answer?
I'd make a movie similar to The Secretary in terms of tone and theme.
Story would be about a guy in his 30s who's a "daddy" to 4 or 5 ABDL women. None of them are involved with him romantically and none of them live with him. Despite getting to live out his sexual fantasies, most of the time he feels lonely and isolated.
Eventually a romantic subplot would develop between him and a vanilla woman whom he introduces to the fetish, at first reluctantly, but later successfully and this causes conflicts between his personal life and the women he is a caretaker before, because they rely on him for emotional and sexual release.
It would be a dramatic romance, and explore the emotional and sexual needs of the characters. It could be done on a low budget, and would hopefully draw attention from the artsy, indy film crowd to get attention at festivals and get awards. Hopefully with the end result being that it works to give ABDL some more positive exposure.
Fantasy answer?
If I had a huge budget and didn't have to worry about anyone watching it besides myself I would make a few things.
1. Just regular programming where all the characters are super-attractive and really thickly and obviously diapered. Sitcoms, dramas, and reality shows. Especially stuff where the focus is on sexual situations and the cast is mostly women.
2. Commercials for various baby products like diapers, wipes, powder, food, etc. except with sexy women in place of the babies in the commercial.
3. Something like children's programming but with the cast all being beautiful diapered women who also find themselves in various sexual situations.
Something along the lines of the muppet babies show where the show alternates between the goings on of the characters in their house playing together and the imagined adventures they go on.
4. An ABDL animated movie with really high quality production values.