I believe that the future of Zoos lies in expansion. As it has been said before, Zoos need more room, and there are certainly many places, at least here in the US, where land is decently cheap. The issue, as has also been said before, is distance. Sure, you might be able to get a nice, cheap, 500 acre plot with the perfect climate and landscape, but if it is 3 hours away from any major city, nobody is going to show up. How do you solve this issue, well there are several ways.
For starters, Zoos/ Safari Parks can survive on their own even if they’re far away from urban centers, that is if they have reputation enough. San Diego Safari Park is quite a ways out of San Diego, but it attracts massive crowds on a daily basis. This is likely because it is associated with the San Diego Zoo brand which, in the zoo world, pretty much guarantees a good facility, and experience.
Now here we start to get into the more hypothetical range, but here goes anyway. Zoos, especially those far away from urban zones, could begin to develop partially as theme parks. Perhaps if some aspects of theme parks are meshed with zoos, they will appeal to a wider audience, and create a new experience which will warrant and incentivize a day long, or even multi-day trip. So long as Zoos keep their core values of conservation and education, I only see a few reasons why this may not work. One issue is that theming is expensive, as with most things, and would require a larger budget. Second, some may not like the cheesiness and over theming of a theme park incorporated into a Zoological facility. However, each of these issues can be solved by gradual theming. Perhaps one or two little rides, costing a bit less money, and a more natural theme, and both of these issues can be kept to a minimum.
Another possibility, is hotels at Zoos. Increasing amounts of Zoos are creating overnight stay programs, and even some like Pairi Daiza are incorporating full blown resorts. Granted, not every zoo is funded by a billionaire, but something on even a smaller scale would allow guests an overnight stay and ease of access when visiting. Whether it is a true zoo enthusiast looking for a holiday, or a simple family looking for a staycation, this concept could yield increased attendance and, in the long term, funds for zoos. A pool, lounge, and decent rooms is really all you need. Perhaps a VIP package for an included Animal Encounter, and you have, just like that, attracted more guests.
Ultimately, I think that using these ideas, and many others, Zoos located on the periphery of metropolitan areas can attract the guests and income to support them. Call me an Optimist, buy if some random summertime fair about the Renaissance can get millions of Coloradans to drive 3 hours out and back, then so can a Zoo.