For Cats, we already have Arahbo, Roar of the World, and while it's a great commander, Arahbo more supports a Go Tall strategy whereas a lot of the best Cat Tribal cards promote Go Wide (Feline Sovereign), which Rin and Seri support better
You can even copy a Proliferate trigger to rack up extra film counters, if that three-time use restriction is getting you down
Each booster may contain Collector Booster-exclusive card treatments, like extended-art cards or even an ultra-rare headliner card featuring a special foil treatment
Plus, since they're all only one color, it'll hopefully lead to straight forward gameplay, since you won't have to worry about mana fixing
Still great in artifact/enchantment, enchantress decks, but those are narrower than decks that play instants and sorceries. #6