It's arguable whether those are actual ponies. In some philosophical sense. Urgh.

As for the Featureless Plane of Disembodied Dialogue, I suggest you use the same tricks as the animators of the show did. Have the characters move around. Sit down. Get up. Interact with the environment. At the window or sitting on the stair. Blowing candles. Sipping coffee. Silhouetted. Glancing. Breathing lightly. Combing out their hair. Little ponies... are a wonder... At their mirrors. In the garden. Letter-writing. Flower-picking. Weather-watching. How they make a maaan siiing...