I am not sure how to bring that, but, will the skill be able to evolve with the society and/or technologie?
In real life, some people have to learn new skill "line" volontary or not because of the way economy goes or other reasons. Or some skill "line" become useless because of new technologie, like in the industrialization period where a lot of old time worker have to learn to work with machine instead of old tools... Also, If a group decide that some line of working is a wrong way of doing thing.
Will all the time and ressource spend in this skill line will be lost, or will be there a way to "convert" some "point" in other skill line? (or even, maybe there could be some way that other player help or compasente in the loss of usefullness of a player)
I hope i am understandable...