Around the time of The Sims 3 Island Paradise, we had gotten the ability for one household to own multiple homes in The Sims 3. You could switch between the lots whenever you wish.
This system already exists in The Sims 4 via buyable community lots. Can you please make it possible to own multiple homes?
I know of a workaround if you don't mind doing it that way. You could always buy a retail lot and just never open the store, rather just have it be another house. The only thing you need is the cash register. When i'm making a lot and i don't want to have their requirements (i.e the register) i shrink the required items as small as possible and hide them in other objects, plants or trees.