That's a single proprietary option from a single vendor with its own storied history of both poor privacy and poor long-term hardware support. (I believe they've effectively bricked the first generation of their routers already!)
It's so much smarter to just not have smarthome devices on the network, and have a single interface or bridge which acts as a security barrier.
I think many routers have a simple feature to restrict internet access for a device on the network. I simply highlighted a consumer product (highly recommended by tech sites) that many average consumers may have.
This is not a realistic view. Most users do not mess with the settings on their router. Most, do not have this feature either. This isn't a good or practical assumption to make of most home networks.
It's so much smarter to just not have smarthome devices on the network, and have a single interface or bridge which acts as a security barrier.