I've only seen Barbie once. (Since it was a somewhat controversial movie, maybe I should mention that I didn't passionately hate it or anything. I've just never really felt like rewatching it. ) But I remember the score-by which I mean the parts of the soundtrack that weren't pop songs-being very effective. Actually, it's kind of ironic. I love the script for Greta Gerwig's Little Women, but I don't find any of the other aspects of it special. The script for Barbie doesn't do much for me but I thought the filmmakers made it work as well as it could. 

I really hope Mark Ronson is just going to do a "normal" score for The Magician's Nephew and maybe a pop song for the end credits and that there won't be continuous pop music throughout. I think Ronson is probably capable of doing what I wish but I'd feel much more relaxed if the movie had a "normal" soundtrack composer. I just don't think of pop music when I think of Narnia. 

Not gonna lie, Mark Ronson definitely wasn't on my Narnia bingo card for this year, even given his prior work with Greta Gerwig on Barbie. That movie its such a stylistically different film to everything we've seen so far from The Magician's Nephew, and the musical nature of Barbie, being part traditional score, part pop music mix-tape, and part Broadway musical, definitely lends itself to a music producer with such an eclectic pop music sensibility as Mark Ronson.

However.... i guess if i was going to make some sort of argument in favour of a pick which is as "outside the box" as Mark Ronson, it'd be the fact that the Magician's Nephew contains a scene whereby a Lion sings an entire world into existence. For something so weird, and out-there, i'd have been extremely disappointed if they did a generic operatic score, given that i've seen that sort of scene play out tonnes of times before.

Therefore, i don't think @Fantastia's reference to Daft Punk's Tron score is too weird at all. That's easilly one of my top 10 favourite film scores, and part of the reason it works so well, despite being a perhaps unconventional choice, is that the marriage of subject matter and music style is just so perfect. Another recent-ish (and somewhat unconventional) score i'm a big fan of is Trent Reznor and Atticus Ross (from the band Nine Inch Nails) score for The Social Network.

Whether Mark Ronson is to Narnia, as Daft Punk is to Tron remains to be seen, however i do think there is something to be said for going in a completely unexpected and innovative musical direction for a scene such as the creation of Narnia. It has to be something so musically inventive that it transcends audience expectation.

Therefore maybe there's some method to the madness? Maybe?

There's plenty of nice pre-rocknroll music from the 50s, very tuneful and pleasant.  If some of that is available (out of copyright) it would add to background and end music. I'm not keen on very modern songs or music being used as a soundtrack to leave the cinema.

He's obviously talented, but I definitely don't have too many thoughts on Ronson as an artist. I'm not even sure how much of his past discography can be used as a predictor of what Narnia's score will be.

I am quite looking forward to seeing who he selects for the movie's inevitable "inspired by the movie" album though... Dermot Kennedy and Ed Sheeran are artists I'd like to see involved