I've come across those mostly in fibre-to-the-home environments. People replace their troublesome ISP-supplied gateway boxes with an SFP+ device with integrated GPON/XGS-PON/whatever directly in the one device. That goes into the gateway/router/whatever. That's a whole different can of worms though. A very special can of worms.

It's not something I have the pleasure of considering in a docsis 3.1 area. Two blocks away: yes, but here: no.