The community doesn't have to answer to WotC/Hasbro about what content goes into their mods, until or unless WotC/Hasbro sends them a cease and desist notice. The community doesn't have milestones to meet for content that is supposed to be in the core game either, meaning content that has been approved by WotC/Hasbro. Comparing what the company can do with what the community can do is apples to oranges. The community isn't responsible if something in the mod leaves the game unplayable, and I have seen mods, installed some even, that have broken games in the past. What Larian should do is exactly what they're doing; focus on the product that they have designed, and make any changes that their team has found need to be made through the various channels, be that direct feedback, or gameplay metric tracking. Pulling a team off of their currently assigned duties to look at what the modders are doing shouldn't be on their list of priorities at this stage of development, and frankly, I'm surprise that they allow mods, since some of them can change the game significantly from what they're currently testing.

Now, it could be that they are allowing them for the express purpose of doing something along the lines of what you suggest as well. "We'll see what mods come up, and if we can work them in, somehow", or some such. Some items shouldn't be all that hard to do, but as you mention, this is supposed to be playable, and it isn't like we're testing it weeks before release. They need time to iron out bugs, polish, possibly even voiced dialog that we're currently missing. Working on cutscenes, and lip sync, fixing clipping details in cutscenes and elsewhere, etc. etc. There's a lot of stuff on their plate, including however many more chapters there are to the game.