Can you explain your concept more clearly? Do you mean simply attacking a target you are facing, the closest target, or manually selecting a target each time you want to attack it with a mouse over?

If it's the former, you just screwed over all ranged classes. If it's the latter, for those of us who do not use the mouse in combat, it's a non starter, and I believe there's already a lot of work you can do with mouse over targeting in the custom macro system.