I agree with Orca.
If there would be a #55, it shouldn't be about the Animorphs (I mean Jake, Cassie, Marco, Tobias and Ax... if we suppose they're still alive).
I'd prefer Yeerks or Crayak Chronicles, or about the Pemalites or... I don't know but #55 seems useless.
The best would be the re-writing of the last 2 books with more details. A longer ending.