I would fully expect to pay more, or be responsible, for cabling inside my house. My main concern about FTTP is the exterior mess that seems to be acceptable.
I guess going into this line of business would change things significantly for Hyperoptic and the others. People generally are very particular about aesthetic things in their homes. As soon as they went into this business, they would need an army of builders, painters, carpenters etc. slowing installations down with endless powwows with homeowners about the choice of paint and materials etc. and handling complaints of substandard redec work. It would only take the most pedantic 1% of customers to bring their business to a complete standstill.
Which means this part customers probably should keep doing themselves - but as I wrote, if you take this route instead of their bulk standard installation, they try to be as flexible as they can. They even offered to schedule the installation to such a time when our builder was there had we wanted this so that their engineer is there doing the cabling.
Not sure what you mean about external cabling. Our Hyperoptic installation does not have a single external cable. Fibre comes to the building in underground conduits. We have two buildings with flats in each of them. They dug a conduit under the courtyard to conceal cables between buildings. All cabling to the flats go in risers. I guess if no risers are available, they are left with no other option but to do it externally. If there is a conduit or a riser, they were happy to use it and we did not have to pay them anything for that or the courtyard digging either.
Curiously, in our building, BT lines seem to be external. There is some kind of a gadget or thing on one of the external walls and all BT lines come from that.
I don't think FTTP means external cabling if there is a reasonable alternative available. If residents do not demand it or the building is managed by non-residents/council who do not care, it might be a different thing. In our case I managed the installation and I never had to argue with them about anything. They offered external cabling first, I said no and suggested using existing conduits and some digging between buildings and they were fine with that. They just sent engineers to survey the risers and the courtyard and then another team to do the digging.