One of those things that sounds vaguely plausible in theory, but turns to crap in the real world. Speaking as someone who has a lot of neighborhood cats, there is no way to accurately identify a "feral" cat from a domestic cat that's just out on the town.

I don't see anything in the original article about a real threat from attacks or rabies. Threats to domestic animals in rural areas are mentioned, but there's a big difference between a cat stalking your birdfeeder and wild dogs going after your farm animals.

My Dad handles birdfeeder-stalking cats by tossing a small firecracker into the yard (not directly at the cat.) My grandfather routinely plugged "varmints" on his farm, but I don't think feral dogs were ever an issue. Cats, half-feral even if they lived there, were a plus on a farm.