This is a lot better than having to download a marketplace map to play a world with custom features, especially for survival add-ons for example. Playing a survival world with mods that has a pre-built castle for spawn and hidden command blocks just isn't the same as playing in a brand new survival world with those same modded features.
I think marketplace maps are required to have some kind of structure/build in them, so if you download a marketplace map that has mods in it and is meant to be a survival world, chances are it isn’t going to feel like a realistic, legitimate long-term survival world. A lot of marketplace maps are meant to have structures in them of course, but a structure being the bare minimum requirement in a survival map that is completely centered around mods can kind of negatively affect a player’s experience on the map. It can make the world feel less personalized for the person playing it
It is cool to see official add-ons added to Minecraft Bedrock; great feature in my opinion
I think that add-ons could bring forth some new creative possibilities to the game. Creators will be able to make some unique and interesting mods without there being the possible setback of having to create a map to go with it