Good question. The change was coming, but it's still a better formulation and I recommend to keep using it.
In an EPA diesel emissions test, anything that gets caught on the exhaust particulate filter is considered "soot" and therefore "bad." Sulfated Ash is a measure of the detergents in engine oil, phosphorus is a measure of the antiwear additives, and sulfur is a component of the base oil and some additives. If the engine has any oil consumption, the tiny amounts of these additives are also consumed and subsequently trapped on the particulate filter to get "counted" as soot. To meet emissions with a diesel, the diesel OEMs are pushing down the levels of additives that if consumed, "count" as soot. This is different than in a gasoline engine where the phosphorus affects the catalyst peformance; in a diesel filter the additives simply contribute to the total soot.
The good news is that it allows the oil formulators the freedom to vary detergent, phosphorus, and sulfur levels to get particulate exhaust down to the acceptable level. In a gasoline engine, there is no leeway; there are simply limits on how much phosphorus is allowed. Diesel oils will still have more antiwear additive than gasoline oils and frankly, they have more detergent than you'll need. So it's still a much better choice.
We will have to wait to see what the next engine oil categories after this bring.
