A hyena might not be a bad shout actually, that same area where the margay lived used to hold an aardwolf.
The long term plan for the cat's row is for it to be completely demolished for some sort of free-flight aviary for macaws, but that's like very far in the future. I think they could stick with their current 'native' theme and make some habitats for Eurasian badgers, lynx, pine martens, and possibly owls, but I doubt that will happen
Edinburgh Zoo is definitely a lot more lacking than it used to be, which is kind of a talking point on here. Just ten-twelve years ago you could see warthogs, maned wolves, addax, gorillas, olive(?) baboons, and a lot more. But where I think they're lacking nowadays is reptiles, I think all they need is one big one like a crocodilian, monitor, or constrictor snake