Some new news on the famous people-sim is that it will have built-in mod support right out of the box. I'm sure they will continue to sell new mesh-based models and items through an in-game store, but the ability to mod and tweak the game comes with the game - something very few games can say in the current day of micro-transactions and in-game purchases.
The people over at Simsvip.com have the scoop:
Everything the community makes is astounding to us, super inspiring, and it is interesting to see what people come up with. Please continue doing it as we want to be able to encourage and foster that creativity because it’s so important to what The Sims means to everyone.
We cannot officially support and screen everything that comes out, so it is very important to us that we set up a good foundation that can help the community manage what they’re creating, and communicate to other people how to responsibly get involved in the modding and creating community.
• Directory for Mods in the user data folder.
• Custom Content Technology Document with data formats that will help creators avoid conflict with what has been done in the game. This document will be expanded on as we go along.
• Dedicated Modding Section section on The Sims 4 Official Forums for feedback, discussion, and issues.
• Game options panel contains section for mods. (Script and Non-Script)
