If you can stack macros up on two keys, you could probably get away with it. I'd still think the cognitive dissonance would get you killed more often than not. There's a reason most people who play more than one prefer to multi than to control each. I did two-boxing like you're talking about for a while with a hunter and shaman but it ended up being a serial thought process for me. I could move the mouse over a big button and basically click it when I needed a heal but doing complicated stuff just needed too many keys and far too much positioning/strafing/etc.

For me, the benefits to fine-grain control over both was far outweighed by having the keys all on one kb/mouse and just having the 2nd guy on follow and /assisting me. Not to mention that it sped up my killing quite enough to make up for the extra time it took to mouse over to the other guy and loot stuff.

[edit] BUT, if you're dead set on doing this, may I suggest pet classes? Hunters and warlocks do well at this as they can DPS without having to maintain melee range and can control PVE mobs well with the pet taunts. In PVP, I wish you the best of luck. :P