If I want to learn a new skill -- say, the ability to write legibly -- my project might be 'complete transition to easy and legible writing' -- my next actions would be a series of drills repeated daily.
Something that you repeat daily for a period of time really seems like clutter on an NA list. Perhaps it belongs somewhere else?
And when do you declare that you 'have' the new skill? Do you have to define a 'level' and once you reach that, you can decide whether to continue or not? Is there a known 'form' for setting levels?
Perhaps projects and next actions are simply not the places for improving skills and abilities, or for acquiring new habits?
Maybe they are goals? Where do they fit into GTD?