Earlier Robot Framework mapped FOR loops internally to keywords and this approach was also used by Testdoc. Now that we also have IF/ELSE structures, we have been enhancing the model (#3749) and nowadays there are separate objects for representing FOR and IF constructs. Testdoc still internally only has keywords, though. The reason is that it makes showing all steps easier and this same approach is also used by log.html created during execution. I'm not sure is changing that worth the effort and it certainly won't happen in RF 4.0. The reason I don't consider this high priority is that both Testdoc output and log.html are to be opened on a browser and how data is represented internally is pretty much an implementation detail.

Although I don't think changing Testdoc in this regard is worth the effort, I'm not against someone else doing that and providing a PR. I also think having a way to convert a test suite structure into JSON would be handy in general, but such functionality doesn't need to be tightly tied to Testdoc. We could even make it so that same JSON data could be used as input for Robot.