What I thought of was the ability to charge--either independently or together--the spells of each hand, in order to eliminate "lower level" spells. Instead of having multiple Fireball spells with varying damage ranges, there could possibly be a single Fireball of which damage is determined by skill level and perks. In addition, this Fireball spell could be charged by holding down the button assigned to that spell's hand. While this Fireball hand is charging, the other hand is free to fire off a different spell, such as Lightning. Or, if both hands are assigned Fireball, a single most-powerful version of Fireball could be charged with both. Even further, one hand can be assigned Fireball and the other--assigned a different spell, such as Lightning--could be charged with it, combining the spell graphic and effect of each. This combined "Lightning Fireball" would arc out and, if it hit its enemy, could do a great deal of instant damage, damage over time from the burning of the Fireball, damage or drain the magicka of the target, and/or produce a knockback effect--a benefit of charging and combining those two powers. This ability to mix-and-match and blend spells could represent a replacement to spell-making.
Effects could of the charges and blends could vary almost indefinitely. Lightning and Blizzard could significantly slow or freeze a target in place, slowly depleting their magicka reserve. Telekinesis when combined with a projectile spell such as Fireball or Lightning could increase the speed at which the projectile fires and/or guarantee a knockback. Drain Health--if limited to a Touch range--and Lightning could produce a sustained ray of lightning that drains both health and magicka from the target. Charging will vary anything from duration, power, or even the spell's aesthetic look.
For checks and balances to this system, the mage when charging could be limited to reduced speed or a standing position.