A zoo that was going to be based on cold weather and native species was going to be built in my city in the 1960s but never came to fruition, sadly (starting at page 186) Unbuilt Hamilton What a pity. I think it would have been a success, had it been built (though competition from Toronto and African Lion Safari etc which display more exotic species would probably end up hurting it though). This zoo geek would probably have visited it every week
Two (at least) in Las Vegas, Nevada (USA). The old four acre Southern Nevada Zoo, now closed by government authorities, had bought a large parcel of land just outside the city to move to. This was mid to late 1990's. The Irwin's of Zoo Australia had planned something in this city as well that never came to fruition. One in Casa Grande, Arizona (USA). For a few years there was a billboard on Interstate 10 with a protruding cutout of a giraffe and a sign saying something like Family Fun Park and Drive-Thru Safari coming soon. The plot of land is still vacant and there are these weird baskets on pillars (big enough to hold a couple people) that are still there. One in Charlotte, North Carolina (USA). This thread details plans but nothing came of it. New major zoo to be built? Also Jim Fowler's place at a resort in Georgia, etc, etc
In Germany, there were many plans for a satellite-zoo of Zoo Frankfurt (e. g. Nidda-Zoo) but none of them was ever built (beside a one or two exhibits in the starting phase). Although not a zoo but a marine park, SeaWorld had plans for a park at the Arabian peninsula (one of the UAE, afaik), but this was not realized.
New zoo in Poznan has big, circular former military fort on its grounds. There were plans to make a huge circular exhibit showing everything from invertebrates, fish, amphibians, reptiles, birds and mammals to great apes. They were never realized, although the fort apparently still stands. Zoo Warsaw once planned a building for elephants and elephant seals. The plans were adapted to the current elephant house.
Bristol's new zoo Wild Place was meant to have a much more grandiose opening and was meant to be a lot larger. Also, does anyone remember Biota(?) in London's Docklands which was due to open around summer 2012 to coincide with a certain sports event?
I was driving in southwestern Ohio and saw a sign that said Safari opening soon, but this never happened as I went back by to see and the sign had been removed and the house demolished
How strange -- must have fallen through somehow. I think a zoo was planned about 15 minutes from my home, the owners had a few exotic species for the time (elk, bison, llamas) in the 1980s, the animals were rehomed when the couple divorced.
I can think of two examples from Denmark: A group of young zoologists/biologists intended to open a zoo with a focus on Oceanian species in Aarhus - Denmark's second-largest city - back in 2007 or so (Aarhus is the only one of Denmark's major cities to not have some kind of zoo or aquarium, even though it used to have a small zoo that closed in the 1960's). In the news article I read, the municipality claimed that they considered the project to be plausible, but in the news video I saw, these people just spent most the time joking around with each other instead of giving proper answers to the interviewer's questions and didn't seem all that serious about opening a zoo. After the initial news articles, nothing was ever heard of the project again. A much more serious project was "Tropebyen Slagelse" ("The tropical town of Slagelse") which was a big tropical zoo - similar in size to Randers Regnskov, I think, but with one huge dome instead of three - meant to open near the town of Slagelse. It was clear that the people behind this project were passionate and serious about opening the zoo as they choosed a favorable location, hired architects, opened a fancy website, talked to other zoos, hired a "development" team, did all sorts of fundraising campaigns etc. The project started in 2006 or so, and the zoo was meant to open around 2016/2017. Until 2012 or so, there would regularly be progress, but then nothing was heard from the project in a few years. In 2015, a press statement was sent out, mentioning that the people behind the project deemed it too unrealistic to raise money for such a huge project, and the project stopped.