My understanding of it is also pretty surface level, but I was not under the impression that it develops "expertise" in a particular subject matter, at least not in a way that's easy to harness. From what I've read, it develops expertise at the token level.

Because the natural continuation of this is to say like, "Ok I want to load the bird detection expert and the navigation expert but leave the medieval European history expert behind", and my understanding is that this is not really how it works. At least at the moment.