The only argument I can think of is that Sky expect to make themselves the dominant financial power in the sport, such that their demands become more important than any other stakeholder. They'd then use that position to develop the sport into what they want, and use that to turn F1 into the sort of product that has mass appeal. But with F1 teams having budgets around £100m per year in the midfield, realistically Sky would need to be contributing 20-30m per team to lever that situation. 11 teams across 6 seasons makes that a £1.6bn outlay. When you factor in that FOM/CVC will cream an awful lot off for themselves, for that amount of money to reach the teams, you rapidly approach a price that could perhaps buy F1 itself, never mind just the TV rights for the UK! So if that's not going to work, then its got to be a power play versus BT. Only you've got to think they've bet heavily on the wrong horse. MotoGP, WEC, even Formula E are all seeing rising audiences, whilst I'm fairly sure I'm correct in saying the worldwide F1 audience is dropping.
It depends if they obtain the rights to sub distribute through alternative broadcasters in alternative countries.
They have a deal with TSN in Canada, but I would assume TSN have to pay FOM themselves for broadcasting rights for the live feed, and then pay Sky a small amount for providing commentary and analysis.