It certainly needs to be remembered that everyone pays for the power consumption of the port at the DSLAM today; it is just hidden away within the money you pay your ISP, and they pay on to BT.
For reverse-powered G.Fast, it becomes an explicit issue that might have to be separated out...
Was that cost split between four properties, so a max of £20 a year, if so I would be ok with that, but not sure about £80 of electricity. Suppose it would depend on the cost of the service as well.
The standards that have been written to provide reverse power generally allow for up to around 15W to be used, but examples I've seen suggest nearer 10W being used. Per port.
Over a year, 10W maps to 90kWh. At 12p per unit, that's roughly £11. About £1 per month.
Could this be handled by BT offering two wholesale prices that differ by £1 per month?
For comparison: In today's FTTC DSLAMs, a fully-populated 288-port Huawei consumes 600W, or approx 2W per port. About 20p per month of today's bills.
Note:
As chipsets take advantage of better manufacturing capability, power requirements generally drop ... so there is merit in waiting for later iterations of the hardware before plumping for a design that is to be reverse-powered.