Would they/he/she be a separate species because in my line of thinking they're a half breed: half pony, half griffon? What does everyone think? What does everyone think of hippogriffs interacting with ponies and essentially being a half breed?

5349926 You know who you should ask about this? MLP-Silver-Quill

5349926 Funny you talk about Hippogriff's, because that's one of the origins of the Hippogriff, though true to all myths and stories many things change with each retelling/imagining.

5349926
Georg's writings play with the idea, as a pony/griffon mix... though a live hippogriff hasn't actually appeared in them so far I think.