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That "Ethernet over CATV" was aka GM-MAP (General Motors Manufacturing Automation Protocol).

My memory is fuzzy on the details, but Data General played around with it very briefly, and Chipcom spent more time developing it as a product. The advantage of cheap infrastructure was perhaps offset by the fact that it wasn't Ethernet, it was, I think a token-passing bus, 802.4, because the nodes couldn't see each other's transmissions so collision detection was problematic. One set of frequencies for nodes sending data up to the headend, then a frequency translation and a second set of frequencies for sending data down from the headend.

The cable companies actually used it when they started to morph into ISPs. It's all fiber now, or should be.

Funny story: I've had internet over cable as soon as it became available. Though a series of companies have owned the physical plant. First a local company named "Cablevision" (aren't they all?) which got bought by AT&T, then sold, then sold again to Comcast.

A few years ago, Comcast sent me a letter telling me I had to exchange my modem because they were upgrading and the one I had would no longer work. I pulled it out and noticed the ownership sticker had AT&T's name on it. Comcast sent me a new modem, told me they did not need me to return the old one, and then, three months later, sent me a bill for not returning it. I grabbed the AT&T modem, hustled down to the Comcast storefront, handed them the AT&T modem and demanded a receipt for it...which I copied and attached to the letter they sent, and returned THAT! Nothing more was heard. Except that a month later, they jacked up the monthly modem rental fee another buck, and I bought my own off Amazon, returning the one they'd just provided. No difference in my service.