Well that suggests that they are using compact SFP's or cSFP for short. Not something I have come across before. Not unreasonably because although I deal fibre all the time with work for the last 15 years, cSFP's are a very specialised thing only available from a few vendors and their use case is not really relevant at work.
Basically a cSFP is two BiDi SFP's squeezed into a single SFP form factor. This works because the SFP standard was designed to allow two LC connectors for your normal transmit and receive. BiDi put both transmit and receive on a single fibre at different wavelengths. As a normal BiDi SFP only has a single LC connector a cSFP can put two BiDi SFP's inside the physical foot print of one. The advantage being that you double your port count on switches which saves physical space and cost. That said I pity those having to cable up a 480 port cSFP switch. Mind you I am not sure the cost savings are really their as cSFP's or two channel BiDi as they are also called are very expensive, £85 for two channel BiDi SFP at fs.com
versus under £10 for a standard one.
However reading the available keymile documentation it is just a plain BiDi ethernet connection and consumer premises equipment is basically a standard BiDi media converter, and you could replace it with one of your own or a BiDi SFP directly in a router. The tick will be determining whether you need a 1310nm or 1490nm (it appears cSFP's dont come in the 1550nm variety). You could either examine the Gigaclear equipment or for an extra £10 just buy one of each and try till you get link
Then it will be a case of working out what they are doing to establish the layer 3 connection. I guess the options are PPPoE (would seem daft to me), VLAN tagging, DHCP options, or possibly 802.1X. Thinking about it one of each would allow you to put a cheap managed switch with a couple of SFP ports in front of the Gigaclear equipment and turn on port mirroring and easily see what they are doing to establish the layer 3 connection.
I very much doubt that the layer 3 is established using some propriety protocol, because it would be a lot of expense for no benefit. The layer two would appear to be standards based however.
I would say for someone so minded it would be possible to ditch an Gigaclear provided customer premise equipment. I know I would be