The board of nursing in my state has been trying to develop a logical solution to this for quite some time. The trick is basing it on acuity not just numbers. The "how" is the lingering problem. Since this is a situation that, depending on unit/location/environment can vary literally by the minute, it is tough to even regulate such a thing.
It is an important step in the right direction, but unless some kind of incredible system is put into place I see it as nearly impossible to measure and even harder to enforce.
Just my 2 cents.