Animal Kingdom is an interesting Disney World resort park. At its core is a natural theme that isn't as prevalent at other parks. But what really sets it aside from the other parks is, well, distance.
To get to Animal Kingdom, you either drive or take a bus from your resort. There is no other options and that makes your day of hopping parks a little less likely to include Animal Kingdom.
Let's start over at Magic Kingdom. Here you will find the central Transportation Station that will get you into MK or onto the monorail to go to EPCOT. This is a perfect set up for park hopping between EPCOT and Magic Kingdom.
The best and easiest park hopping option is from EPCOT to Hollywood Studios. You have four maybe five ways to get from each park to the other. The Skyliner is the easiest, most relaxing, and far more enjoyable way. The 15-minute or so ride gives you a great look at other areas of the Disney property and resorts. You could also take the ferry boat, drive yourself, take a bus, or yes, even walk it as it isn't that far.
In one day, you could literally visit Magic Kingdom, EPCOT, and Hollywood Studios but you can't add Animal Kingdom to that and you likely won't replace one of the three with them.
This isn't to say you can't visit Animal Kingdom and another park. You absolutely can but you are going to take a bus which is typically overcrowded with sweaty parents and irritated kids (I know because I'm the parent with kids) or, you could drive your car to another park...this is the preferred way and yes, I have done both.
Over the last decade we have watched construction at all the resorts. We have seen the installation of the Skyliner and watched as new upgrades have been installed and new worlds like Pandora and Galaxy's Edge come to life. Yet we still don't have an easier connection between AK and the rest of Disney's resorts and from those at Disney I have spoken with, there is nothing new on the horizon.
Connecting AK to say, MK would make sense. The best option would be a monorail. The distance between MK and AK is similar to that of MK to EPCOT so a monorail would make that trip an easy one. Imagineers and engineers could route the rail south of the park to avoid animal life in the park.
Another option would be a monorail option that connects with EPCOT. The two parks are closer in proximity than Magic Kingdom is to either one but the best option may very well be a gondala that connects AK to Hollywood Studios. Let me explain further.
In the above Tweet, we see two images. In the second Google Map image (the white one) we see all four Disney World parks. Clearly MK is pretty far from the others but we also see that it is only a 4.5 mile difference between Hollywood Studios and Animal Kingdom. That distance is much shorter when we apply the "shortest distance between two points" rule.
In the first image we see the same route but we cut out MK and EPCOT. Just to the right of the words, Disney's Hollywood Studios is the Skyliner. The Skyliner hub is located outside of the park enterance. From this point, Disney could easily add another route that would move across the parking lot to the south then across the marshlands to Animal Kingdom.
In doing so, Disney would interconnect their entire four parks together. Guests would be able to traverse the parks without having to drive their own vehicles thus cutting traffic around the parks. Visitors could plan their days ahead of time to park at their final destination and begin their day at any other park of their choosing so long as they have the park hopper option.
Ultimately the question is why? The biggest reason is that Animal Kingdom closes typically at 8:00 pm and the other parks tend to be open later, sometimes as late as 11:00. Most guests can complete a day at AK in half a day so having the ability to quickly move to the next park would be ideal without having to take the bus system.