The OP's case is an interesting one. There is no good reason for the airline to ask the customer's permission as after all they have only purchased one seat.

If all pax were considerate FT'ers then of course, let everyone be upgraded. I'm someone who lowers his window-shade, has acceptable personal hygiene and when inebriated keeps quiet and passes out in his own seat with his clothes still on. There are unfortunately many flyers who do the opposite, while bragging loudly on the in-seat telephone about how they got upgraded.

I'd probably ask more about the customers to be upgraded, to make sure I was not opening the F cabin to screaming children (or adults)...