This is the perfect solution from the customers perspective, But I think Apple would prefer the profits from selling a new phone rather than the profit from replacing the battery for you.Best customer experience: Make you think your phone is too slow so you buy a new one. How about a message on the screen informing the customer that the phone is throttling back to avoid battery failure. "You should consider a new battery from your nearest Apple Store. Would you like to have Siri create an appointment for you?"
Conspiracy theorists may wonder if Apple offered Futuremark some sort of inducement to produce the report a few months ago https://www.macrumors.com/2017/10/06/apple-doesnt-deliberately-slow-older-iphones/ but as we know they would not do that, but some people might think it.