Interesting. If I was asked to design such a class I would focus on action types. A 1[w]+stat isn't exciting as a standard action but becomes encounter power worthy if its an immediate interrupt and daily power worth if its a free action. In this regard, you have a decent number of action types to work with. Here's a breakdown of heroic tier balanced powers for at-wills:
Standard - 1[w]+Stat plus bonus (push, slide, 2nd stat dmg, daze, etc), 1[w]+stat to area, ongoing effects like stances, polymorphs or auras
Move - shift, switch places, jump, fly, etc... (look to monk full disciplines for balance)
Minor - +tohit, 1[w] or stat dmg to next attack for striker; increased area or effect to next attack for controller; heal or buff to next attack for leader; mark or +def for defender, etc.
Immediate Reaction - shift when hit, mark when hit, minor effect when move adjacent, etc
Immediate Interrupt - stat dmg when hit, defender style reaction to ally dmg, minor amount of movement in response to enemy moving near
Obviously, these are just examples. I think the first class I would try to build this way would be a striker as they are easiest to balance. You're going to have to build a power replacement system similar to psionics so the number of powers doesn't get too unwieldy. I'd go for at least 3 attack powers, 2 minors, 2 movements and an Immediate at first and not add more than 3-4 to that total number.
Keep in mind that someone is going to have to play this class, so don't forget to make it fun. Since most of their turns will be less spectacular than other classes, you're going to have to add enough flexibility to keep them exciting.
I like the idea though. What a great super tactical character class. Like a super monk.