Fully agree here. I wouldn't want to see a lot of species crammed into a small amount of space.
I'd rather see a well designed, well immersed and ultimately, well spaced precinct. That's what makes the Islands idea the most appealing to me, especially as they already have the right tools for it (space, proximity and species).
If we consider an additional three islands to be present, that could create plenty of space for multiple Orangutan families, some of which could coexist with the Saimangs and potentially even White Cheeked Gibbon.
I do like your idea of the Sloth Bear mountain, but I'm just not sure Melbourne would go and import Sloth Bears from overseas. They've shown no indication to do so, and nor have any other zoos within the region. Steve Robinson stated the regions still keen on Sun Bears so take that as you will. Just thinking realistically, but would very very much like to see Sloth Bears at Melbourne!