I recommend a weekly basis for the premium shop rotation as opposed to bi-weekly/every two weeks. I get that premium cosmetics aren’t everyone’s cup of tea but this at least increases the chances someone will see something they like.
Also makes sense to add more stuff to the in-game currency shop. Weapon skins, uniforms, the like. Warhammer is fantastic in part because of the many factions and it’s cool to get their stuff in Darktide.