I don't want to derail, but I think its worth pointing out that the historical basis on which this comparison is based is somewhat flawed.
Much of Princess Diana's really global popularity came after her death. Indeed, the idea that, as the OP says, "her transgressions only make people love her more" really wasn't the case before her death. While her charitable work and campaigning were admired, a sizeable chunk of the British public were growing sick of her bitter wranglings with Charles and had reservations about her seemingly extravagant lifestyle. See, for example, the rather unsympathetic brief reference she gets in the British House of Cards (season 2).
Her death changed everything - it was only this that really allowed much of the population to see her as an idol and ignore the more difficult elements of her character. Much of her appeal was, as the historian David Cannadine has pointed out, that once she was dead those groups in Thatcher's Britain who felt they were outside of the mainstream (disabled people, the gay community, the poor, etc) could graft their own aspirations and ideals onto Diana without fear of her actions contradicting them.
This isn't going to be the case for Marie-Antoinette. Once the revolution starts in 1789 her death is always going to be seen as something of the old order, even in the best of circumstances, and hardly something that large sections of society can attach personal and poignant meaning to.