I do have some "almost-perpetual" projects, but they are not of the self-development type. I separate my job into three areas of focus: research, teaching, and work (sometimes called "service" in higher ed). Work includes all kinds of things that are ongoing, such as committees I chair or organizing a public lecture series. Almost all of these are things I've taken over from someone else, and plan to pass on to someone else at later date. I think of them as "ongoing projects" that sit mentally just a bit above projects but below areas of focus. I don't want them to be areas of focus because they just aren't that important. I could break some of them into recurring projects semester-by-semester, but planning and scheduling is essentially continuous. I still get the happiness bump of completion when I can close out a semester, so I don't miss the act of checking off a project.
As for implementation, in Omnifocus, these ongoing responsibilities can be single-action lists. In programs with tags or equivalent, like Things, they can be simply tagged as "Ongoing."
Maybe this approach can be used for personal development as well, but I don't know.