While it is very true things could be changed in future updates, as they often are, I'm on the side of sloths being in WE. As many have stated, they hardly move, especially this species of sloth. I can absolutely understand being bitter about them not being habitat animals, but there is just not enough versatility with the animal itself imo. Swimming would be super cool to see, but what would be the point in a zoo setting? Granted, the same could be said for the proboscis monkey, but unlike the sloth, they don't take an hour to move twenty feet and have to suffer through the janky climbing. Using the koala and the tortoises is a poor comparison as well. Those animals, while janky in their own right, realistically actually move places and are faster than the sloth.
From a gameplay perspective, it also just makes more sense imo. I don't want to deal with 30 notifications from my sloth who's starving to death because its food isn't directly beside it at all times, or build a habitat that's like 5 foot wide with an entire ugly gate attached to it (null gates when?). Also, with the null paths, we can make more convincing pseudo-habitats by playing around with turning all of the walls to null too. That's what I'm planning to do myself. Yeah, the animations are gonna be looped and yeah, the sloths will probably teleport to random points within the box when you look away like the other exhibit species, but that doesn't mean you still can't make it work. Personally, until the DLC releases, I don't see any issues with this choice given the species they went with and the current state of climbing in general. If it was the two-toed, then I'd feel differently. My stance could change, though, once we actually see the sloth in-game.
The only downside to this for me currently is there likely not being baby sloths. That isn't the end of the world for me, but I'd still mourn that they aren't included. But again, as mentioned, this does not mean they can't be included in an update in the future.