Nice idea. Didn't CfB (or someone else?) mumbled something about "in the future we can make great things with account numbers" which would mean, a big adoption rate of your idea would interfere with this "great things"? Damn, can't find the post... and no clue what it meant...
I just read the post, that such a system should be done on client side. So I designed mine to be client-side and not interfere with the NXT protocol itself.