So am I reading it correctly that the new venture would be using full fibre instead of the DOCSIS 3.1 network?
It should be made clear I think that this new venture is separate from Virgin Media as is required to avoid Ofcom's wrath.
It's an entirely new thing and will not be an RFoG / DOCSIS network. It'll be a PON network of some description. I frankly wouldn't be surprised if it were an EPON network as EPON supports provisioning via DOCSIS -
https://volpefirm.com/epon/ - and is a great choice for wholesale networks. GPON doesn't really have standardised provisioning methods which is why Openreach don't mix ECI and Huawei OLTs and ONTs while with DPoE it's standardised.
That it makes it far easier for the anchor tenant, Virgin Media, to provision services over it is of course just a bonus.
I think people would be surprised if they knew how many of VM's TV channels are now delivered via IPTV over DOCSIS rather than broadcast. It makes no sense to deliver over broadcast when each addressable area is only 32 premises as with an EPON split.