To solve the issue of the inability of players not being able to make full use of their dlc they purchased I would like to suggest a slot for dlc or bazaar skinned building items be added to the building piece selections of the construction hammer. This slot would only be lit up if the player either owns the dlc recipe or if another player trades them skinned pieces.
This could be done by having both being required to have construction hammers in hand at the same time and that would allow a building piece trading slot to be opened if they were also near each other. The dlc owning player would select the trading slot on the building piece selects in the construction hammer menu and then select the dlc piece they want to create. The dlc player creates however many number of pieces to be traded and then again selects the trade box that would be filled with the created pieces.
The player seeking the dlc pieces would need to select (highlight) the trade box in their construction menu box that had the dlc pieces offered (only one trade box would be selectable per player per trade) and press the confirmation keybind button (separate from the normal placing one) and now that many number of pieces will be available for creation by that player providing they have the materials to do so (the dlc player need not have the mats to create the pieces as they would not be the one placing them.