There are bodysuits with plumbing zippers in the "right" place, but I've seen them on people and the zippers are more often than not unfortunate and scary. They sit very uncomfortably against body parts and often call attention to that spot rather than hide anything. And, I'm not sure how practical they are for anybody except men.
If the costume has a full one-piece suit with no hint of a waist seam, and would look really awkward as a two-piece, it's hard to suggest making it as separate shirt and pants. I've done it for costumes that have layers on top which can be moved or removed easily in order to drop trou. But if you're looking at a superhero bodysuit with no way to break it up into a top and bottom, you kind of just have to make the bodysuit and budget yourself extra time to go to the bathroom.
For armor and such, sometimes you just have to bite the bullet and expect that when you have to get out of the costume, you have to get out of ALL of the costume. If it's still comfortable to wear, and there's nothing in the design or function of the costume to allow for separating top and bottom so you can only remove bottom layers, then shrugging and accepting that it's going to take disassembling is about all you can do. If it's a really uncomfortable, heavy, or cumbersome costume that you might not be able to wear for more than 2-3 hours at a time, then it's sort of a moot point because you'll probably need out of the costume before it becomes an issue. BUT...if there's a place in the design where you can change your layers so you don't have to take off the entire thing, work with it.
An example: my Magician of Black Chaos is not a pleather bodysuit but a shirt and pants, so I can take off the bottom half without completely disrobing. The belt and the straps that connect the rings from neck to hips hide the place where the shirt tucks into the pants, and are made so those detach from each other but not the suit. So if there's a belt, or armored structure, at the waist and hips, depending on the entirety of the design, you might be able to do the same.
Founder and Vice-President, Madison Area Costuming Society, a chapter of the International Costumer's Guild
Strange Land Costuming - www.strangelandcostumes.com