I think any big contributions are likely to come from HPMoR readers who are attracted to LW, become a part of this community, and then go on to do good stuff. HPMoR is just the gateway drug.

Then there's the more diffuse sanity waterline effect of lots of HPMoR readers becoming somewhat more rational, and more receptive to big important ideas wherever they encounter them. Sci-fi has had that kind of effect on the development of a lot of people here, and this story can extend that kind of influence to a new audience via Harry Potter. Plus, in this case Eliezer got to fill the story with the ideas and themes that he considers most important.