You got me interested but Im still thinking about that x-ray vision idea :D Sure, echolocation is possible with blind people but thats because we already have that skill. They just managed to intensify it and learned to process the information better. You can already tell where the sound is comming from and you can hear different reverbs of defferent spaces aka sound bouncing back from surfaces.

But x-ray vision is a different beast! We can only see narrow spectrum of visible light which cant go through objects. UV and IR are not doing any better. There were experiments in which they made retina of mices react to infra red thanks to chlorophyll so they gave them temporary "nightvision". But if you want rays to go through objects you are left with radiowaves or gamma. The two extremes on opposite sides of spectrum. Since there cant be any external device emitting these rays the question is how much gamma is around us already.. and even if there was... solid objects tend to absorb smaller doses of radiation rather than it would just fly straight through.

Anyway, thanks for an interesting theme :D