I'm sure a lot of people would be happy to pay a couple of quid for a cosmetics pack with relatively low development costs. New objects with the same effects as previous ones, new decorative objects for indoors and outdoors, new floorings, etc. Things like carpets, actual kennels, vending machines with shop effects, chess boards, table tennis and gardens (jobs and food source). Maybe a few fun or handy features borrowed from the more popular PC mods.
I know you want this one, Nat. 
http://twinfinite.net/2015/10/the-10-best-prison-architect-mods-you-need-to-play-with/19/