Could be more interesting for hard-to-reach underwater sensors. Water attenuates RF quite severely, but is good at conducting ultrasound. The response would have to be in ultrasound, too, of course.

5) These can be great if you want them to be monitored, but if I'm using my wife's toilet when I'm not supposed to, I'll simply hold the disk when I lift the seat.

From the artwork it looks like they're targeting industrial use. Seems like a low grade replacement for bar/qr code scanning. The "wearable" (more likely integrated into some other thing than worn IMO) receiver seems to point in that direction too.

Author probably has a specific use case in mind. Probably some application where EM emissions are undesirable or power is complicated that has thus far resisted automated industrial data entry. Investigating the use of something like ultrasound would align with constraints like that. Someone (department head? PR department?) said that was too niche and to make up some bullshit with mass market appeal.