The idea that I had for how they could introduce new ships is if there were a class mission that every class runs where they're in a space convoy or something and they get ambushed and the ship is destroyed and they have to use the escape pod in the ship. Then the player would be introduced to the option of purchasing a new starship. all the old ones would be available for purchase again. If you wanted the same ship again it would cost little or nothing to replace, but if you wanted say The Fury on your Bounty Hunter you'd have to pay extra. Then they could also introduce, say 4 new ship designs that would be available to every class and both factions.
I've always liked the idea of being able to decorate the inside of you ship too. Like having something for your achievements, or maybe some art on the walls.