I have an idea for a variant magic using class that is simple and uses XD. I call the class the Mage.
Basically all the combat magic for the class would use XD using the same progression as the fighter. The most basic use of the XD would be a single magical attack that would require an attack roll and would do the damage of the XD.
Each Mage would pick a primary damage type at character creation and all damage done would be of that type. A single XD could be spent on an attack to change the damage to another type. When a saving throw is required the damage type would dictate the stat used. For example, fire and force could require Dex saves, poison and cold could require Con saves, psychic could require Wis saves, etc.
Then I would have the following maneuvers available for use (using 4e tactical rules).
1) Blast - spend one XD to make a blast 3 attack with damage equal to the remaining XD. Each target can make a saving throw to avoid the damage. This can be a blast 5 if you spend two XD.
2) Burst - spend one XD to make a burst 1 attack with damage equal to the remaining XD. Each target can make a saving throw to avoid the damage. This can be a burst 2 if you spend two XD.
3) Missiles - split up the XD available to attack multiple opponents. For example, if you have 3 XD then you can make three 1XD attacks, or one 1XD attack and one 2XD attack.
There could be other maneuvers that could add rider effects (such as pushing and knocking prone) onto attacks.
The Int modifier would be added to all attack and damage rolls.
For non-combat magic they could cast rituals.