You can't write spec banking on a set specific actors. Pine may not want to go back to TV, he might not want to be Kirk after the next movie. You never bank your story on the casting.
That's one of the first things that struck me in the OP. Stephen Fry ? Why call it from the get-go ?
There's really no need to be rude, though, Seer
because Stephen Fry fits the profile of April to a T. in terms of attributes and resume. the same with Felicia Day as Colt.
why... it's about being ready and having a vision (and names) to present, just in case.
can it be re-worked? yes. if it has to, but not on anyone's directive but the actors or studio.