Most games with subscription services are MMOs where the subscription gains you access to areas of the game, like worlds in Sims. Some also allow you to purchase worlds. If you let your subscription lapse your character is only allowed in free sections of the game and those you have actually purchased.
It is hard to see how this would work in Sims because our Sims don't go on adventures to other worlds; they live there. Also Sims expansions include CAS and Build and Buy items. In subscription games these are either free or additional purchases (often microtransactions).
All in all, a subscription based Sims game sounds like a very different experience from what we are familiar with.