Time to be cynical...
I don't see an Animorphs movie happening anytime soon. If we're really lucky, we might get a throwback that turns out to be of good quality, even if it isn't entirely true to the originals (See Transformers).
The problem is that, as of now, it's a niche series, with two distinct sides. We have the young side that the series was intended for, and the more mature audience that delves deeper into it, like ourselves.
Based on film maker stereotypes, if it were made animated or like a cartoon in any way, it would be more geared to the younger audience, as a simple fact. There are a few exceptions to this rule, but they are few and far between.
If it were made to be animated, we'd surely lose the battles beyond anything more than near misses or completely survivable or exaggerated blunt trauma that the victim just walks away from.
The more mature the film gets, the more serious it gets, the more it alienates the younger audience. It would be grittier and more enjoyable for us, true, but it would also be live action, most likely assisted with high-quality CGI.
For something as small and forgotten as Animorphs, I find it highly unlikely it would be geared lower, but still with the high quality of larger, more well known films geared to younger audiences, such as Narnia.
There's still trouble. I find that a film geared to younger audiences would not really happen simply because the books are long out of print, and that audience has likely not even heard of Animorphs. The more mature audience is far to small to warrant the budget needed for the quality to make a movie geared to the more mature audience.
This is best realistic possibility that I see: Another ten, fifteen years pass, and Hollywood is looking for ideas. They come across Animorphs, and while it was originally set for kids, they see it definitely had capacity. They decide to go with it, and make a high budget film. It wouldn't follow the plot in any real way beyond using the name, characters, and basic premise.
Basically, what happened to Transformers.
The problem with this idea is that Transformers was on TV, a show that the vast majority of people had some concept of, even if they weren't real fans. They would react to the film by recognizing the title, and deciding to see it out of nostalgia.
Animorphs was a long book series, and if a person didn't read them, they'd basically be clueless as to how things go. It wouldn't have the nostalgia affect on nearly as many people. A large sum of them would think it was based on the Nickelodeon TV show, and decide it wasn't worth a second glance.
You need to remember, filmmakers don't care about having the best movie, just the one that's most profitable. Sadly, Animorphs simply isn't that marketable. We might get lucky with a throwback in a while, but beyond that, I don't expect much at all.
