I suspect this quarters surge might have something to do with...

I suspect this quarters surge might have something to do with the way HFC is rolled out, but i could be wrong about the migration, not sure.

I seem to recall HFC used to be very segmented, there were Optus HFC areas and Foxtel HFC areas, and at least in the initial rollout a decade ago there wasnt much overlap. Internet via HFC was also much faster than ADSL2, but more expensive.

When NBNCo takeover a HFC area, previous HFC broadband users dont see any change technically, minimal disruption compared to copper, its mostly just admin. Optus has a reason to get people to sign up to NBN quickly, before competitors can get their marketing hooks into them, which they had not had the opportunity to do previously for that product.

There would also be a lot of people in HFC areas still using old copper ADSL2 who i think still have 18 months to switch, they would be very unlikely to be Optus customers (who are already on HFC).

So there is an initial surge of NBN signups from previous Optus HFC users, but they should thin very quickly, copper users in HFC area will probably switch at normal rate, and there will be very few Optus migrations.

Another thing to keep in mind is that NBN is planning to roll out a lot more HFC, it is expected to comprise 24% of the mix (according to 2017 NBNCo plan), its currently only 10% of signups.