I can't officially clarify it but I can say with certainty the 4K broadcasts will definitely be over 5G only (Optus have stated this from the outset).
This is due to technical reasons rather than any marketing etc. (I'm sure Optus would love to stream to the 90% of Australians with access to the NBN rather than the 5% (optimistic) of Australian homes with access to 5G.
Attempting to live stream 4K video over the NBN (to so many homes simultaneously) would be unfeasible with the mix of technologies and underlying protocols. Perhaps if we'd gone FTTP as originally planned we might have had a shot :o(
Optus have also said it will only be Home 5G broadband customers (so no mobile) - I'm not so sure of the reason for that though. Perhaps because Optus knows the phone will be switching in and out of 4G/5G mode as the owner moves around they just can't provide a good 5G service. As it is even the Home Broadband 5G offering is still struggling to get a solid stable footprint.
Anyway, no doubt official confirmation (or denunciation) will be along soon.
"Just got off an online chat and the rep Assured me that as long as I have a Fetch Mighty I will have access to the 4K content..."
That’s is unfortunate and emblematic of a lot of Optus Customer Service. They want to help but if you call three times you can often get three different answers. In this case the agent is probably confusing the fact that the Mighty already does 4K content (aka Netflix). That and the fact Optus have said the Mighty will be the only device you can watch the Olympics in 4K in Australia via Optus. They’ve just not added in the 5G limitation.
"I can't see how they'll differentiate between who's using their fetch mighty with a 5g home broadband"
The content stream simply won't be broadcast / available over the NBN network. Optus fully owns its 5G network and controls all content that goes out over that data stream. I don't know but I also suspect the 4K Olympics will be via the Optus Sports app on the Fetch so that will also control what channels you see or don't see.
The mods here are good with chasing down correct official information so you should get an answer soonish.
"Its not a technical issue, its a cost issue (CVC from NBN)"
No its a technical one. The cost of CVC is in itself related to technical limitations on the network (it simply can't handle too many people simultaneously viewing different 4K streams at once).
I believe the technology built into the 5G is essentially to allow one to many broadcasting. So instead of a few thousand households all watching a unique 15Mbit 4K stream on the NBN they can all latch onto a single 4K stream massively reducing data needed.
If you think about it logically everyone involved would like to see the NBN used to broadcast 4K Olympics (NBNCo, Telco, Any broadcaster, Customers, Fetch, The Olympic rights holders etc.). But I think they've all agreed (except us) that reliable 4K transmission from Japan is just not possible unless its over 5G. Telstra has obviously decided to pass but Optus is big on 'sports' and presumably got the 4K rights for not too much outlay. It will definitely drive interest in their 5G network but IMO its just as likely to backfire when 95% of those interested are told they can't have it even if they wanted to.