I've been reading a lot about this project over the weekend, all of it critical. There's a good bit by Sian Cain in The Guardian here which discusses some of the sloppier aspects of the project - images of the wrong author on the cover page of one title, and a dodgy attribution for Edith Maude Eaton/Sui Sin Far (her sister Winnifred was also a writer who used the pen name Onoto Watanna). Their pen names celebrate their Chinese heritage (their mother was Chinese, their father English).
I had heard of Onoto Watanna because I know one of her descendants, the sisters work undoubtedly deserves more attention, but probably not because one of them might have written one story under a make pseudonym. Catherine Taylor has more excellent points to make in this article in the TLS, particularly around the reasons people chose pseudonyms.
I'm willing to accept that the concept was well intentioned and not primarily a bid for sales, although the number of errors these articles point out make me wonder how much of a passion project it really was - but I'm still wondering who ever thought this was a really good idea.
I'm all for feminising the canon and reclaiming the very many women who have disappeared from it, or never been allowed a look in despite how good they are. So it's fortunate that we have publishers who are literally dedicated to doing just that, as well as an increasing number of women represented in what I can't help but think of the classic classics ranges from Penguin and Oxford World's Classics. For women in translation Pushkin Press are a good place to start looking.
I also think we could be doing a lot more to reclaim genre writing - especially romance which is probably where you get the most women writing specifically, if not exclusively, for women and often using pseudonyms (although they're generally female) to differentiate different strands of writing as a name becomes a brand. It seems to be just as common in detective fiction too, and almost from the beginnings of the genre.
I have thoughts about this in relation to fan fiction too, but they're messy and are resisting being written down. Essentially I keep coming back to the thought that reclaiming names, possibly against the preferences of the authors in question, helps nobody.