I think it highly probably that the recently announced Plusnet prices are close to being the answer, whilst still allowing a reasonable profit margin.
I don't know where you read that EE have 30 million mobile customers, but given the population of the country that seems a little high. Even allowing for a fair number of people with more than one mobile. Many of whome may have an old Orange PAYG SIM lying around with a few quid in - as I do. I also have a Virgin one in the same state, that I was forced into to get the deal I wanted on a handset.
I think it highly improbable that EE are thinking of anything like "several million", given that after several years of decline from the Orange peak their latest published figure that I'm aware of for broadband connections was 714,000.
Connection - Plusnet Extra Fibre (FTTC). Sync ~ 54.0/14.9Mbps @ 600m. - BQM
"Where talent is a dwarf, self-esteem is a giant." - Jean-Antoine Petit-Senn.
Allergy information: This post was manufactured in an environment where nuts are present. It may include traces of understatement, litotes and humour.