Also if we're twenty years from simple Aliens-style exosuits, then we're fifty years away from anything close to a military combat application.
Honestly though, as awesome as I think they are in fiction, in reality they might end up snapping spines like twigs. :\
There's some really nice prototypes out there and none of them really backfire in any way. There are tons of safeguards on those things.
I'm a mechatronics graduate, had the chance of working with a Raytheon Australia exoskeleton back in uni. It was very impressive, we were all the type of nerds who loved Iron Man when it came out. You're probably right about the limited range of motions, but they'll likely remove the tethering by a decade. Don't ask me for the technicalities of it though; I barely passed my control systems classes much less be able to work on exosuits
I did see a Japanese exoskeleton which was very impressive albeit a bit slow. But as with Japanese style robotics, it was used to help cripples move around instead of military applications. They showed it off with a person who was partially paralyzed, even gave him some very impressive strength.
I agree that these things are not going to be used in combat situations any time soon. Most likely they'll just be used for logistics and construction will be the first to buy them. But hey, who knew that we'd see the Wright Brothers flying thingy evolve into the machines that dropped the deadliest bombs in history and sank the Yamato? Who knew we'd go from ENIAC to having a digital library in our pockets more advanced than the thickest encyclopedias?
At this moment exoskeleton development is already well in the prototype phase. They just have to work on power supply and the thing lifting its own weight. I'd bet that they'll be a world changer, much like trains and aircraft were, given a few decades of development.