They will still be staggered throughout Season 2.
There should be folks on hand for emergent issues, but unlikely swathing changes, until early January.
The items available in beta will likely be items already in-game which can be purchased for Shillings. This is limited in so much as new cosmetics not being available, and no premium items either. ( @Don_Kanaille called it!)
Provided the player owns Vermintide 2, they can opt in.