I am doing more and more with Javascript frameworks (bablylonJs, a 3D webgl game framework, KendoUI Javascript controls, etc.) The nice thing about their documetation is that they not only describe the api, but also have a online playground (like DOJO, JSBIN, JSFiddle, etc.) where you can see how feature works.
Here is my brainstorm. For some of the more confusing transformers, eg. FeatureMerger, what about a limited FME cloud driven space which gives you a JSBIn like framework where one can see an example of how the transformer works? So that it does not cost you much $$ to leave up. It could be restricted to a very limited data set, and only be one transformer linked to a "online version" of the Data Inspector.
All the levers I would have would be to change the parameters of the transformer from the default demo to different values so I could play with it?