The handheld railgun isn't held back by it's own technology, but by logistics. They'd be too dangerous to transport by plane because the magnets mess with aerial navigation systems, hence why the Navy is where you see them the most, and the fact that their obvious advantage is very linear and kind of at odds with the ongoing reduced focus on infantry. However, they would have the advantage of allowing a soldier to effectively carry possibly 10 times or more the same amount of ammo considering that they can do way more with way less. Think .22 sized cartridges punching as hard as .308 or more, but whether that makes up for the increased weight and need to have yet another specific caliber is up for debate.

I see anti-tank railguns as much more likely. Possible even mortars.