I'm not asking to be 2 classes at once, but the way it is now, you have to chose a path and stick with it to the end.
You don't get a chance to try out anything else. For that, you need to create a new toon and start over.
We arent talking about Wow with his 3 different roles (perhaps if ever possible useful specc is a role its up to 10 or so) here you have so many options with the weapons and ground/space used abilitys, that its not so easy just to relevel a char.
And its not a new class then you get another ship, dont forget, episodes could get challenging later, and then its important that each class is in his ship , because escort is for damage and tactical will make most damage, science is for tricks, and science will have the tricks (perhaps the weakes specialization need of the 3) engi has tanking abilitys (the activated clas sspecific of course, like tactical) and so he will be the best for cruiser.