About the Echo (Spoilers)

[Enkidoh]

The thing is, there are plenty of people being awoken to the Echo all the time, they just don't understand what it is and so, out of shame or horror keep it to themselves (this was specifically mentioned back in 1.0 that those being awoken to the Echo would often face persecution and harrassment by others simply because they did not understand what the Echo really was - hence why Minfilia ran the Scions' predecessor organization the Path of the Twelve, it was a place of sanctuary for those awoken to the Echo and also show the mundanes of Eorzea that Echo users were not to be feared by sending members out on missions that would benefit the citystates). Cases of the Echo being awoken in people seem to coincide with the lead up to a Calamity however, but again why that should be is unclear.

As for the sky shower seen at the beginning when the player is awoken to the Echo, it is still not known exactly what that is meant to be represent, other than it was there even in 1.0 (long before SHB's story revelations were even thought of).