Progressive learning for apps in general is definitely an improvement. That being said, I don't agree that roping off functionaltiy is the best way for advanced text editors to lower the learning curve. Contextual hints are a better way to introduce shortcuts for those sort of apps.

I also disagree that HN's downvoting feature is an example of progressive learning. It's more about controlling trolls and setting expectations in the community. You have to earn your keep before you can negatively affect change. It's a feature of the meritocracy, not of the usability.