I can't remember who it was, but one of the highest MS bods said in front of a sizeable audience, 'The free upgrade of W10 is permanent'. 'No charges, ever'. Unequivocal, and said in one of those sincere voices that make you think, Does he mean that?
I was aware we don't own the software, but then there was always the established conventions that one assumed would be kind of honoured. Kind of, is about as good as it gets I suppose.