They made a dev blog about this - Classes in Darktide
Which, ended up partially being an absolute joke.
While similar, classes are not the same as careers (in Vermintide). Some of this will become clearer as you jump into our Closed beta this weekend, but most of it won’t show up until the full play experience closer to launch. More specifically, you can expect a deeper narrative experience, greater range, and more options in character customization. There’s also a more profound and wider progression in weapons.
This was basically a lie.
But yes, they’re planning more. unsure if they’ll be paid DLC or free. Which means that it’ll be paid.