I honestly didn't think this would happen, because as popular as the book series were when I was a preteen/teenager it did kind of fade into obscurity with the rise of other book series that gained way more traction and popularity. Add to injury that the books eventually became out-of-print, so most probably didn't know of their existence until recent years with the notice that all of the books are available to read for free online. However, it seems like things are turning around, from the books being made into comics to this movie announcement, this is precisely the resurgence that we've been needing! Although I do question whether or not a movie is a good medium for such an adaptation, considering all that it entails and I fear that it might be watered down too much and it'll be considered too similar to the YA material that's come out in recent years to be noticed and therefore flop, which is why I kinda wish it was more of a long miniseries instead, but this is still exciting news regardless.
Also, it's worth mentioning that unlike a certain other author, K.A. Applegate is actually an ally, she also has been incredibly supportive of the fans and their personal interpretations, theories, and headcanons of the characters and books, even acknowledging that she could've done better in terms of representation when she wrote them.
And yes, I do recommend anyone who hasn't read Animorphs to do so, it may have been a kids book series but it never shied away from the dark subject matters, and it did get very dark. Body horror, murder, death, cannibalism, war, psychological trauma, it's all there and it's great.
(It makes me wonder if Everworld will ever get noticed, not just for an adaptation but just in general because it is often overlooked, it truly is the underdog of KAA's work imho.)