The Diana movie with Naomi Watts was a flop even. For the youngsters of our time "Diana" is already history. It is possible that "Wallis" will remain more in the history books, since a King once abdicated for her, than "Diana" whom, in essence, will be a footnote as the first wife of Charles and the mother of the two Princes.
The whole "Diana (or Camilla) will be a footnote in history books" statement always makes me cringe.
This is not how history books work. History books focus on a subject and discuss it. They tend not to relegate people into the footnotes unless they only played a very minor part in whatever the subject is, but even then they're more likely to not be mentioned at all than simply put into a footnote.
If a history book is written on the history of the British Crown, comparable to say David Starkey's
Crown and Country or Mike Ashley's
British Kings and Queens then many consorts will only have a brief note on them - Queen Anne's husband, Prince George of Denmark, for example, doesn't tend to make a big splash in such texts. This is because the overall role that the consorts played isn't necessarily a big one in regards to the historical narrative. George of Denmark didn't have a huge role in an overarching history of Britain. Some consorts, however, are rather noted because they did play a big role - Eleanor of Aquitaine, Elizabeth of York, Catherine of Aragon, Anne Boleyn, Wallis Simpson, etc. These consorts are focused on a lot in such history texts, and really it's very likely that both Diana and Camilla will receive a similar amount of focus as Catherine of Aragon and Anne Boleyn. Their roles, their shared history, is one that changed the monarchy.
If a history book is written even more narrowly about Charles himself, then neither Diana nor Camilla will be in the footnotes. If it's about pop culture or major events the 80s or 90s, both women stand to be mentioned, especially Diana. There was an American program not too long ago called "The 90s: The Last Great Decade" that spent time focusing on both the divorce and Diana's death.
Historic figures aren't simply relegated to the footnotes. At least not outside of a high school textbook which deals with everything in such broad strokes that it's impossible to note relegate important things into the footnotes.
I'm not sure that I agree with that assessment, Duc_et_Pair. I think she'll be remembered for the upheaval she caused the BRF in the 90's, even if not for her more positive attributes. She'll also be remembered for being the mother of royal line, even though she was never Queen Consort, and that makes her part of history. 
