Breezepelt. The anxious, angry black tom would be interesting to know more about. 

Storm. What happened when she left? How did she feel about Gray Wing? And how did the whole den collapse?

Darkstripe. Did Tigerstar really accept him easily when he went to ShadowClan?

Willow Tail and/or Red Claw. It would be cool to see their hatred for each other in their points of view.

Violet Dawn. What was her relationship with Slash like?

Star Flower. Looking through the sweet and traitorous she-cat who broke Thunderstar's heart but completed Skystar's life's eyes.

Whitestorm. Snowfur and Thistleclaw's only kit, Bluestar's nephew, and Firestar's first deputy. If only we could get his point of view.

Shadowstar, Riverstar, Windstar, Gorsestar. All of the leaders who we never heard enough of.

Turtle Tail. The pretty she-cat who was Tom's former mate, then Gray Wing's, and died trying to reach her kits.

PebbleheartSparrow FurOwlstar. Turtle Tail's kits, raised without their father Tom, but their foster father Gray Wing.

Silver StripeSlateBlack EarWhite Tail. Gray Wing's mate and kits who we never saw enough of before he died.

That's about it, even though it is 22 cats.