Mastery, or the building of skill, is one of the core intrinsic motivators called out by SDT and while many games seek to simulate mastery (RPG progression systems, etc.) games that seek to or require that the player build real skill have very niche appeal (with a few notable exceptions.) We have a better understanding than ever before of how skills are acquired and how performance can be improved, we should be able to do better design for mastery!
There is a lot of good research into how humans learn new skills that points toward processes and mechanics (like structured practice and spaced repetition) and there are a few games that have broken through to a large audience that focus on mastery (League of Legends is probably the largest) so it feels like there is plenty of material to work with on this topic. Additionally this group could focus on taking lessons of skill acquisition and apply them to general tutorializing even for games that are not mastery based.