Because of this I can't imagine them taking on the responsibility of another person's code and repairing it if and when it breaks. So what happens when mods break? Who's responsible for fixing that? Bethesda is a business, they're going to do what's best for their shareholders.
What happens when mods break each other? I'd bet my right nut that the majority of people who've ever modded a bethesda title have had a mod cause crashes, whether from start up, when going through a door, or picking up a cheese wheel. But I do have a few concerns about the long term health of such a system. I'll be honest, I don't know a whole hell of a lot in regards to the deal that bethesda/valve offered modders when they initially tried to implement this.