I don't see either with the potential to be a kage. I believe their rolls are defined by their parents (in Neji's case his uncle), Shikamaru becomes Konoha's lead tactician/jounin commander (as his father) and Neji may even break the branch traditions and lead the Hyuuga clan, but in honesty even though both are respectable shinobi, smart, and, to a certain extent strong, they don't have the potential to rise in their skill to kage worthy shinobi.