Your suggestion requires numerous entirely new art assets, animations, game mechanics, and likely a fair few script hooks within the engine.

This is the kind've stuff usually reserved for content patch, and significant enough to justify creating a whole new job class to implement. Contrary to Hollywood's depictions, programming is not like wizardry, where a guy taps the keyboard in mystic patterns and magically the desired thing happens there and then. It's on THAT basis the idea can be fairly safely discarded, at least within the context of replacing the entire summoner class with it