I know its a bit early for a question like this since obviously nobody played the game still, but i want to roll a Knight Enhancer which menas i'm basically going from ranged (Mage) to melee (KE), does this mean i won't be able to use my cool long-ranged spells?
No, it's not likely that restrictive. KE will likely have 10 abilities, a mix between passive, active and sustained, to unlock. With those sustained abilities active, likely for a defense buff and a summoned weapon, they most likely will just take up a large chunk of your mana pool thus limiting how many spells you can cast before you run out and have to wait for your mana to regenerate. Also not having a staff equipped will also probably reduce your spellpower and whatever other stat buffs they normally come equipped with so that will affect how potent your magic is as well.
But I'm just guessing on most of this, we really don't know all that much about the KE, let alone the other specializations. Even the normal mage schools are kind of up in the air since they've reshuffled them quite a bit from DA2.