Uhm, there's a few fights with the Scions... think it was Alphinaud at one point? They say something like, "I can sense the aether swelling. Get ready for an attack!" Then a group stack AOE marker goes out. So it's something that can be sense by people who can manipulate aether or any magitek device that detects aether as well, as far as AOE markers go.
The Gladiator questline has Aldis remark on, "watch how she fights; it's not exactly high theater." or something like that, so there's also the physical reading that we do.
As far as the Echo buff in combat goes, it's most comparable to the Blessing of Light received from Hydaelyn during the Ultima Weapon encounter. Basically, you're supposed to be destined to beat the fight, so your power swells up with the Echo. But this buff is also implemented by the devs on old raid content automatically without any wiping required for things like Binding Coil and Savage Alexander and such.
In theory, if we could control the Echo, then we could use it to view the past of our adversary to see exactly how they fight and to know all of their moves, since viewing the past is what our Echo does. Of course, not all of our adversaries are combat veterans, like Tsukuyomi, so it's not really for reading moves. I coulda sworn though, that there was an aspect to it that made Echo blessed individuals more proficient in combat. Better able to sense aether swells and things, maybe?
