If you look at that illustration, you see that it's not just one ethernet connector, it's one of these massive connector stack with one ethernet and 2 USB, also, it adds quite a bit of depth to the connector; it must have been made with one particular brand/type of motherboard in mind.
Still, if these are in the wild, then perhaps our chinese friends might have reduced the footprint even more to the size of one connector.
I know the connectors with integrated magnetics are quite a bit 'longer' and 'beefier' than the passive ones.
And you don't think such a device could be made quite a bit smaller today, with better manufacturing support?
I'm thinking it's entirely plausible that such devices exist, and are broadly in the wild. Mostly targeted. That said, our own govt (US) is not innocent. Neither are China, Russia and many others. It's what government espionage actors do.
I think it's a fault of many that US mfg has fallen off as much as it has, and that critical infrastructure would allow foreign mfg in general. Or at least final inspection and assembly internally. Not just the US, but most countries.
