So perhaps a periodic purge mode (written into the logic) would suffice, maybe just timed or employing CO2 sensors? CO2 is a highly politicized compound right now, so all of this discussion about integrating sensors into vehicle systems is taken with a grain of salt for me. Seems like an excuse to gather data (to eventually use for political purposes), similar to data gathered by radar sensors, cameras, CANBUS data dumps etc all in the name of our safety, of course. I'm sure insurance companies will have no use for data that can allow them to dismiss claims.... "for our safety and to save lives"- I just don't buy it.
Nevertheless, a full, proper recirc mode is also something I really value. When driving through the acrid smoke of a wildfire or an industrial accident, fresh puckied fields or just behind the clown in front of you with no catalyst, 100% recirc is valuable.
The dumb nanny systems not so much eg. GM vehicles that lock recirc out and mandates AC on based on the vent mode. That's just ignorant and irritating.
CO2? Hey, the vehicle in front of you is pumping way more of that out than the occupants in your car. Just try not to drive for 5 hours straight in recirc. Doesn't seem so hard, but neither does backing out of a parking spot without 5 radar sensors and cameras.