We're at the end of the Darktide pre-order beta's first week and there's still lots left to be added to the game. Fatshark has laid out the changes (opens in new tab) it's implementing week-by-week with a somewhat vague summary of the features we're getting in the run-up to release, but right now there aren't enough unlocks to be worth the grind.
Over the weekend I maxed my Zealot Preacher to level 30 just to see what features are in the game or if there were any noteworthy or secret unlocks. Except for the cosmetics (opens in new tab) you can get through penances, a few cutscenes, feats, and weapons for your class (opens in new tab), there isn't really anything else. If you reckon you're only going to level one character during your time with Darktide, I would very much recommend waiting until some of the other features have been added.
It's kind of clear from the cutscenes, like at rank 11 with Sire Melk, that meeting certain characters will unlock their respective shop or function for the player, it's just that those functions aren't in the game yet. That said, there are weapon unlocks, and some of them are particularly great. The heavy eviscerator chainsword for Zealot, for example, is one of the best weapons I think Fatshark has ever made, and using the flamer to melt a horde of unsuspecting poxwalkers is a joyful experience.
The problem with unlocking weapons right now is that we don't know how the crafting system works, and what implications it'll have on rerolling, or even acquiring weapons. Every time you get a cutscene you also unlock some new weapons that can appear at the Requisitorium, but will that also unlock them for crafting like in Vermintide 2? Curios are also a bit of an unknown. You can buy them, or acquire them through the curio reward chance you get from equipping curios, but will they be craftable, too? I reached out to Fatshark for some clarification regarding crafting and cosmetics.
It's all pretty unknown at the moment, but the one thing I do know is that I don't think it's worth grinding to level 30 right now. In the coming weeks, we'll have more missions, weapons, systems, and the cutscenes might make a lot more sense. While I am really enjoying the combat (opens in new tab), I think if you want that feeling of progression that isn't just jumping into missions to kill stuff, you should probably wait.