The Horse and His Boy has a lot of interesting background. A series or season centered around the Golden Age of Narnia, give or take a few decades, would make for great storytelling in the right hands. Aravis and Lasaraleen recount numerous adventures throughout the Calormene countryside, while the adult Pevensies outwit giants, literal and political. Juxtaposed are two would-be arranged marriages; thwarting both evades Calormen while strengthening the bond between Narnia and Archenland.
This got me to thinking which of the other Chronicles might translate well as a series, or a season of a series. The Lion, the Witch and the Wardrobe and The Voyage of the Dawn Treader are certainly episodic in nature, although they lend themselves to a distinctly linear progression.
Then there's The Silver Chair. Rilian's backstory suggests enough material and mystery for it's own episode. So do the sequences in Aslan's Country, where Jill and Eustace seem to pass through effortlessly at both the beginning, and at the end of the mission. Almost alongside their encounters with Aslan unfolds Caspian's search for his son and Rilian's redemptive reunion with his father. So there is a bit more opportunity there for bilateral storytelling.
In The Last Battle the subplots are more notably intertwined. The schemes of the Calormenes gradually collide with Shift's shenanigans. While the Friends of Narnia gather to surmise its entire history, the last king of Narnia tenaciously tackles the culminating conquest it finally faces. Help emerges, legends are unveiled, and new worlds are discovered. This makes for satisfying, anecdotal storytelling.
Finally, I would posit that Prince Caspian and, especially The Magician's Nephew, offer still more potential as a television series, nearly rivaling that of The Horse and His Boy. Much of the lore in Prince Caspian does come from the characterization of the Telmarines, and I agree their ambiguous arrival comes a long time (but is not a long time coming) after the Pevensies' unanticipated departure. The Magicians Nephew also offers an expansive timeline to explore the last age of Charn, mettle in the imagination of a young Uncle Andrew, traverse the streets of Edwardian London, and hope for the health and healing of Digory's mother, all intercut with a panning shot of an ethereal Wood Between the Worlds.
I concur that bringing the Chronicles to life demands greatness, as Nicole Stratton of The Logos Theater succinctly puts it. It cannot be turned into a modern young adult drama. It can be dramatic and many of the characters are young, but they conduct themselves in a manner worthy of excellence...that befit of royalty. My belief is that a series or season, especially of certain installments in The Chronicles of Narnia, could work well. Where and when that could happen are the perplexing questions that I hope will merit further reflection and consideration...