Inscription-like the scroll making idea which takes us back to oblivion. I'm thinking maybe the arcane enchanter flips over to become a spell craft table or something.so as your skill improves the spell effect gets stronger similarly to enchanting.Construction-the idea of making war-machines like ballistae, cannons and catapults as well as portable ones such as a kind of Gatling bow or magic turret like the ones in-game.you could make basic ones out of steel and as your smithing and construction skill improves you can make stronger machines.(Daedric Cannon of Death anyone???) these machines could be enchanted too.Bombcraft-pretty similar to how assassin's creed have done it. You would use firewood for splinter bombs, iron ingots to make shrapnel bombs...you get the idea...they would need only one hand to throw and you could make stronger bombs as your skill improves.Adding these skills in dlc could raise the level cap to around maybe 91 because Bethesda are awkward like that
but overall it should massively improve the skyrim experience if the guys at Bethesda take notice
looking forward to further dlc!!