Remembering that old remote controls did used to use ultrasonics,

Actually, they were using frequency that are still inside the human hearing range (for undamaged, young ears). I remember that I was able to "hear" the squeal of the remote of our TV when I was a little kid.

My wife can still hear those "ultrasonic" "cat squealers" that supposedly keep your neighbors cats off your lawn.

The advantage of this almost-but-not-quite ultrasound is that you can probably send/receive it with "audio-type" equipment, instead of having to deal with actual ultrasound equipment. I somehow doubt that ultrasound in the MHz range would be any good for data transmission in air - you'd probably lose most of the energy just trying to cross the solid->air transition in your transmitter.