I can think of lots of ideas. Marbled cat, flat headed cat, bay cat, african golden cat, andean cat, etc...
There really aren't that many Margays left in zoo's here in the US as they are being phased out. There are only two AZA accredited zoos that have them: Sacramento and Santa Ana. There are some private collections that have them though. (I think) However these are good ideas. I'll try to send all of your ideas to my supervisor at the zoo. Thank you guys for the suggestions!
Recently the staff had a meeting regarding ideas of animals to display in this exhibit, even with a lot of ideas, we're still unsure. I told some of the staff your ideas and they said they were good ones and would possibly consider them. I also wouldn't mind seeing Tree Kangaroos in this exhibit.
Here is another idea for this exhibit, Indian spotted chevrotains with Grizzled giant squirrels like Singapore Zoo does