The question would be: do the Larians use certain editors themselves to create the content in BG3? Are those editors standalone tools ready(or easy to make ready) for the masses? If not, it would be way to much work to create exactly that to be used by us.
Though the idea is tempting. Persistant D&D in a world seen in the gameplay video would be a dream come true
It really depends on the process Larian is using. Different people in Larian work on different parts of the game, and so the content they create for the game is not always created with the same tools that are used to build the maps, which complicates the process of building a map. Even assuming shared resources (textures, models, AI, code), there may not be any one single person who has all the tools and knowledge to build an entire map from scratch.
