I tend to agree that making the sugar measurements more robust is worth more than measuring the ketones at all. However, low sugar and high ketones can happen. And just getting notified when ketones pick up can be worth something too. The additional measurement is not useless seen from my perspective.
As an example: I was on a study that gave T1D patients Dapagliflozin (Farxiga). During the study, while on a long hike, I was hovering at low sugar and consequently insulin supply was mostly cut off for an extended period. As I started to to feel unwell, I measured ketones. I was briefed as preparation for the study to measure ketones when something seems wrong. Otherwise I wouldn't have thought of measuring ketones. Might not even have carried the kit.
On that occasion, the ketones were way above 1 mmol/l: a very high value. Protocol would have required me to call the study doctor due to the high level. Since it was a Sunday, I spared her, shot some insulin, ate a sandwich, and continued my hike. I could do that because I was not alone on that hike. I knew that if my situation deteriorated, somebody would be around to call rescue.
At the study debriefing I mentioned the incident and they said that adding to the effect of the Dapa, I was probably dehydrated, which led to the rare situation of both low sugar and high ketones.
All in all I think that if the sensor makers exhaust possible improvements for the glucose, it can make sense to add the ketone measurement as a safeguard. Having high sugar can have many reasons, and it often takes me a while to get to measuring ketones. Getting the signal of rising ketones, I would react faster a few times a year in situations where my insulin supply is broken.