I've though about that too, but I have two issues: First, they still don't make a diesel 4matic sedan (which is what I want/need as a daily driver for my wife). Second, I really don't see much advantage of a modern diesel over a modern gasoline engine in this application. The diesel gets somewhat better mileage, but diesel fuel tends to be expensive and the initial purchase cost is usually higher. Both engines are too complex to be DIY friendly, and I can't imagine it would be cost effective to keep either car indefinitely (other very expensive parts will break long before the engine wears out).