Cadence isn’t based on any specific horse breed, but I did try to keep her build more akin to that of show horses (thin legs, flowing mane and tail). She’s also based on my headcanon that Crystal Ponies have actual gems embedded in their bodies. Cadence’s gems are those on her neck/chest. Her wings, tail feathers, horns, hooves, and ears merely have a cover layer of crystal on them that can sort of act as armor in a pinch. It can chip or crack if subjected to too much stress though.
Shining Armor is based on Shire Horses, specifically dappled grey Shires.
More headcanon art coming soon.