Exactly, we shouldn't stop there, and should consider it a problem if it fails at 15 years, unless there's some kind of severe duty like, oh I dunno, maybe stopping and starting your vehicle every time you stop?
Again, exactly right, which is a reason why owners won't want it, that it's on them to bear the cost.
Why would it be just as well, to have an additional thing fail sooner, somehow justified by other things that cost as much or more that fail TOO? That is the opposite direction vehicles should be going in, not adding one more thing to fail among the growing list.
"A starter and a battery that is designed to do this", in itself doesn't make it a good idea depending on what is important to the owner. Everything in a vehicle is designed to do what it does, but that's not a rationale to add more failure points. If the starter design works better, fine, put it on every vehicle without stop/start, instead. Let the aftermarket starter market dry up, as well as all the other replacement parts that could last longer if not for designs that don't emphasize lifespan enough.
It should not be assumed any longer that there are things you need to replace on a 10 year old vehicle (your # for cost of ownership above) besides the consumables if it's not a severe duty situation. If there are several things to the point where you consider a starter just One More Thing, then I consider that a poorly made vehicle.