Biggest mark against something like this is that all future characters have to be able to fit through current game geometry.
This means all the spawn room doors mainly. And currently, Reinhart takes up about 85% of those door frames. So don't expect a hero to be bigger than him.
Thus, that Spider Chick who also happens to be in this image is way too big to be able to fit through some of the smaller spawn doors:
Rear center
Maybe she can deploy her spider at will when she's outdoors, and eject to fit in tight places, like D.Va but at will or on cooldown?