If you have extremely reliable home internet I suppose it's viable, but personally I've found the redundancy of being able to fall back to hotspotted mobile data when required extremely important.
You can put an external mobile modem and make it a failover wan connection. That way you still control the network via your wifi equipment but have that still available.
What is the faraday cage achieving then? Any device in your home can connect to the cell network anyway. Sure, they probably can't connevt to satellite anymore, but I doubt that it is extremely popular.
I thought the purpose was for ypur phone to be able to connect to the cell network, for example for (non-VoIP) calls. But, if your phone can connect, so can any other sim-enabled device.
No, the comment you replied to seems to be talking about using the cell network as a fallback for Internet access. That's why the stipulated an antenna on the outside of the house.
I was assuming that it meant having their phone fall back to the cell network when WiFi is iffy, and I was pointing out that this would require breaching the faraday cage entirely essentially.