Think it will have to depend on the basis of "Magic" as the class desription for the warlock says they have spent there time studying the traveler to unlock its secrets so if the magic is based of tech then it could be a wearable modual such as gloves or modular armour attatchment that takes the possition of the primary weapon of other classes. So rather than a magic bar as such it would be more of a charge bar that will take time to repenish depending on the indervidual drainage requirments of each spell/tech effect this also adds to charicter specific enhancements as a warlock may look for a better power sauce instead of the titan who may look for a better gun.