I've always been a fan of sending the Giraffes and Zebras to Werribee. Werribee have the chance to hold a very large breeding group, and with the new Waterhole precinct soon opening, they have an opportunity to move their bachelor group there in favour of holding a breeding group on the Lower Savannah. Okapi and Bongo would be suitable replacements for them imo.
The Reptile House is indeed where the Cow exhibit is now; assumingly to tie in with the Butterfly House next door.
I honestly don't see Melbourne building a new Reptile House though. Their current one is a piece of history, and still serves its purpose very well.
Re. The Insect House - I think it's a very interesting idea, but I would like to see it replicated in Growing Wild. San Diego included Insect Buildings in their Childrens precinct, and it's worked very well as children are notably very fascinated with insects. Melbourne should really look into doing something similar.
Okapi and Eastern bongo would be great replacements for giraffe and zebra as Okapi need a shaded exhibit. They’re poorly suited to an open field and they’re a species that people will want to see up close (i.e. zoos rarely give them a large exhibit).
From what you’ve previously said about Melbourne’s troop and from what I’ve seen, the Hamadryas baboons are a popular and engaging exhibit and it’s disappointing to hear of plans to phase them out. I’ve always been impressed by Melbourne keeping a large troop in their city zoo; and hope at least Werribee commit to them.