I'm sure there's plenty of demand for non-rage-based engagement, and in fact there are a lot of platforms that offer that (HN being one of them). I just don't think there's a demand for that on the scale that Twitter wants and needs to operate.
In my opinion, there's two reasons for this; first, Twitter has largely moved mainstream discourse to a superficial conflict-based format, even among those who might previously have enjoyed quiet reasonable discussion; a lot of these people are no longer going to get what they need, emotionally speaking, from a less confrontational platform. Second, the nature of Twitter has brought a lot of people into the mix who were not interested in participating in online discussion at all, but have been energized by the presence of a platform that provides an opportunity to dunk on jerks all day. These people, likewise, are not going to be served by a less-confrontational platform, and are going to move to the next thing or just disperse if no suitable platform is offered.
Twitter is huge; it's scaled for the kind of vast crowds that are attracted by the particular flavor of discourse it offers; if any significant portion of those vast crowds go away because it starts offering a different kind of discourse, then it will collapse under the cost and complexity of running a platform of that size.