That's a tough one. If you want to spend enough money, you can usually put one in anywhere; it's just sometimes it is much easier (therefore cheaper) than others ($$$).
How far away is the nearest hot/cold water supply lines? Where are the vents located? How deep are the joists, and which way to they run relative to where the current drain lines go. How thick are the walls, and are you willing to tear them up to install a new vent? Is the new bath on the second floor where venting might be easier, or do you have to go through 1-2-3? floors worth of walls to do it.
Sometimes, you can't tell until you tear things apart. It is sometimes easier on the first floor, if you have a full basement. If it is on a slab, almost always will require breaking concrete (not necessarily hard, but depends on how much and how deep you then need to go).
If in the basement, or on-grade slab, is there any indication how deep the sewer line goes out to the street? If it is not burried a foot or two, then you probably won't have enough slope to run new drain lines without a sewage pump (to be avoided if possible). But, again, all possible if you want to spend the money and tear things up enough.
So, there is often no easy answer...