How could Kamala being interesting by becoming an Eternal? She is already interesting as an Inhuman and with her current powerset. Turning her into an eternal would complicate things for her.
Only Neil Gaiman was able to make them interesting in his limited series, all other attempts failed as they are practically characters hard to write. They practically have the same power set and are ridiscously powerful that they struggle to interact with the rest of characters of the Marvel Universe.