This would be a bad idea. This kind of targetting would work in a hack 'n' slash game but not an mmo where we regularly have to focus on a particular target...not to mention how picky character and enemy placements can be (although this is being worked on).

The biggest problem with targetting is that when cycling through targets it goes from left to right or right to left rather than nearest to furthest target. Because of this a lot of the time you will target something several miles away instead of what you want to actually target. (This is what needs to be fixed with the targetting issues, not adding a new targetting system every few patches x.x)

However, you can get around this issue via macros and the new keyboard config options. Personally (as a PGL) I have numpad 5 set to target nearest enemy (rest of numpad I have for movement, walking, autorun etc) and this works fine for me mostly. I imagine if I were a mage I'd still be annoyed with how tabbing through targets works though.