In-game addon creator

The ability to create texture packs, blocks, items, and entities in-game would be an amazing feature. Using blockbench and having a simple feature for replacing textures and models would be a sure way to get more people into creating. I was thinking of a system to where you can construct a model and then select what you want the model to be. This way you can make placeable furniture to wearable hats. Now of course maybe not let these go on the marketplace and make them only useable to the people who create them and the people who play with the creator.