Well, you could have a mains powered rechargable battery (or supercapacitor) backed detector. Then again, it better be designed so that the sensor part is replaceable and it fails loud. (Though neither supercapacitor nor nickel-* cells are very expensive, we put them in random MP3 players for $10 a pop.)

The feature richness is a scam though.

The half-life of commodity rechargeable batteries is significantly less than the half-life of Americium.

And people who don't proactively replace smoke alarm batteries are unlikely to proactively change the alarms...changing out an alarm is a bigger job than changing batteries.

A smoke alarm is not a consumer product.

What’s your point? What do you want? Some people are stupid, you can’t change that.