Having read the books and watched the movies (and played in Diagon Alley at Universal Studios, and bored my students with HP anecdotes), I think Keira and Jilly are on to something there. I also think it relates to something else Keira alluded to in an earlier show, which is how fandom and fanon can take over meaning and original source material. Keira was referencing the Sentinel fandom at the time, but I think Snarry has a toehold in Harry Potter fandom because of this issue, too. Writers of Snarry normalized the pairing.
It made me think about my own work. One of my first stories upon my return to writing fan fiction was an adult Harry paired with an adult, redeemed Snape. I had been reading a LOT of HP fan fiction--glutting myself, actually--and I wanted to write a story where they came together as adults after Harry had some life experience. The result turned out pretty well. It's got some minor issues. If you want to read it, you can find it on AO3 or ff.net. It was my first experience writing slash, and dealing with readers who had issues with slash. My give-a-darn about what readers think broke years ago (I started my professional life as a reporter), but it gave me some interesting insight into the fandom that I didn't have at that point.
Keira's points about Snape, however, made me think about why I wrote that story, (see the normalization of Snarry when one gluts on HP fan fiction) and how on earth I could make it work. She's utterly right: In order to redeem Snape, I had to completely rewrite his back story and add information in that the reader (Harry) didn't have as he was growing up. I also had to ascribe a level of insight to Harry that the character, in canon interpretations, really doesn't have and perhaps is incapable of having, given his age and life experiences. I also had to add a soul bond trope in order to make the pair take a second look at each other, because neither would do it with out some sort of dramatic reason to. I had to give Snape an ugly, tragic past as a Death Eater, too.
Wow. The sheer amount of effort that takes.
So, yeah. I agree. Book canon Snape is virtually irredeemable.
Some things, though, I accepted as my personal head canon when I wrote that story. First, Ginny and Harry were not meant to be together. Screw the epilogue. Seriously. In that first story, they married too quickly, then realized they had a mess on their hands. Later stories I've written don't even go there, though I'm not into Ginny-bashing, per se. It's fun to read, though.
Second, the Malfoys could be redeemed. It's not hard to see that most of their motivation in the later books was the survival of their family, and that can be sympathetic. I'm not always convinced that Draco is the best romantic pairing for Harry, either; I've never written that pairing. However, I do know writers who can make it work beautifully without a lot of canon tweaking (cough, Keira, cough).
And finally, I don't think Harry Potter had time as a teen to figure himself out beyond his role as "Savior"--and what an terrible title to have following you around--and in my stories, I like to think he gets that time before he commits himself to a romance that will work. My exception to that, Unexpected Help, follows the Sentinel trope, and Guide Harry meets his Sentinel Tony DiNozzo at 17, but later installments will explore how Harry finds himself in the wake of the war with his Sentinel's support. We are, none of us, exactly who are going to be at 17. We all need to do that exploring and soul-searching.
Anyway, Keira's radio shows have been inspirational and entertaining. Go, listen. I'll be here when you get back.