While I do enjoy rimworld and tynan's model, I don't think it would be a good match for Stardew given how the game has a particular branching story it wants to tell and share with the player navigating choices, where rimworld is more heavily into an (almost) entirely randomly generated story where your long lost brother might show up as a pirate or deceased cousin offended some govt official so now they are applying pressure to your settlement as pay back. The cosmetic option would be a much better fit so players could have alternate options on how characters, tools, plants or monsters appear, to say nothing of the home making segment. Yes mods already make this an option, but the entire point of Cosmetic DLCs is a tip jar for the developer you get something back for, and a way to show your support. New content and story pack expansion by contrast can seriously change the flow of the game and many players do not view them as optional in the discussion.