I think at least for Tim a well written series would sell (or at least would have sold a few years back) without Gimmicks.
The rest of his gen has the problem, that usually the "parent book" kind of defines the ceiling for the books of the sidekicks. If the sales for Superman, Flash and Wonder Woman are not that great to begin with, there is not much of a chance for a Superboy, Wonder Girl and Kid Flash series.
Honestly Black Canary felt extremely out of character in that book, the Rock Star thing came out of nowhere and the art was probably also a matter of taste.
I get they hate live action Robin in these movies, but skipping over the entire journey and development Bruce and Dick have together and jumping to an adult Robin who is basically just Nightwing is so frustrating. It is cutting out such a core part of the whole story.
A series would just work better I agree. You can explore more mundane, everyday interactions in a series whereas you're limited for time in a movie. I'd personally prefer if it was animated as then you'd be able to continue it for years as the actors wouldn't age out of the role, and you can do truly bonkers stuff in animation.
Really I’m suprised at the positive reception. That book wrote starfire as if she was plucked from TTgo. It also has very little substance essentials a slice of life type with no influence on the greater DCU. Which is a common complaint I here about the run of Nightwing here.
Thing is the Dark victory comic didn't really showed that much of the development, and for a movie you would have likely to shorten the story even more.
If you would want show the development over several movies, they would have (assuming they would start with a young Robin) to shoot the pretty quickly one after the other, or the actor would age up to quickly.
That can be done (I think they put out the Harry Potter Movies put out a fairly high speed) but usually they take more time between different movies in a series.
And it might also help the Quality of the movies if they are cranked out at such a high speed.
Dan Radcliffe was already 15 when they shot Goblet of Fire which was supposed to have him at 14, and while the cast did get older, we are still used to Dawson Casting that just 2-3 years older doesn't matter much especially in the later teenage years
A Robin development movie series would be a problem if you actually start him as 10-12 year old and want to see him grow real time, but if you bare it down to the essentials, such as
- Processing grief and revenge
- Treating each other like partner and family
- Growing up and changes
- Fallout and graduation
I think you can divide them between 2 years series of movies, at 12, 14, 16, and 18 years old, just fine.
At 12 it's Robin
At 14 it's Teen Titans
At 16 it's Batgirl
At 18 it's Nightwing
So each big period also introduce something new