Important aspects to the story that were just dropped

[Iscah]

A plot point from Echoes of a Fallen Star was that seeing the burning sky of the final days induces the Echo in some people.

Which didn't happen to anybody during the Final Days in Endwalker and was never even mentioned by any character. Even if there is an explanation (like they neccessarily become terminus beasts because of all the despair) the fact that nobody even thinks of it shows that the writers didn't either.

Simple answer: Hydaelyn was on low battery and not transmitting the "hear feel think" message any more, so even if anyone developed it, we might not hear about it immediately.

Also I'm not entirely convinced that the mass awakening at the Crystarium really was a matter of everyone getting Hydaelyn's signal, or if Elidibus staged that part too. Hydaelyn had been too weak to communicate with us directly for ages.

[Ralphe2449]

Another major one was Zenos dreaming of the final days and Fandaniel going "Could Emet selch have found a way" which was not resolved in endwalker.

More importantly it was near the end of shadowbringers so at that point they have mostly finalized endwalker meaning being cut would be unlikely unless it was really a last minute cut

Though considering it was mentioned that Zenos is an ascian all but in name I can only hope he comes back

[KageTokage]

Simple answer: Hydaelyn was on low battery and not transmitting the "hear feel think" message any more, so even if anyone developed it, we might not hear about it immediately.

Also I'm not entirely convinced that the mass awakening at the Crystarium really was a matter of everyone getting Hydaelyn's signal, or if Elidibus staged that part too. Hydaelyn had been too weak to communicate with us directly for ages.

The Echo is honestly one of the main plot points I'm hoping gets more focus in the future, because while we got some blanks filled in about it, we still don't know other details like why Ancient souls were special and gifted with the ability in the first place.

[Ralphe2449]

why Ancient souls were special and gifted with the ability in the first place.

From memory wasnt that just commonplace, it wasnt something "special" or a "gift", they were naturally born with it. The only reason it is treated special in game is because sundered souls are nowhere near the level of unsundered ones in terms of complete abilities.

[KageTokage]

Not all people can awaken to the Echo, but whether that's because their souls are simply too "weak" post-Sundering to do so or if there's an actual distinction between different types of souls isn't really clear.

The starshowers in 5.3 produced a variety of reactions, with people either awakening to Echo proper, simply feeling a sense of sorrow and longing, or nothing at all, and I took the latter of the three as meaning their souls were ordinary personally; perhaps ones that were born after the Sundering because it's been mentioned souls are both created anew or simply "recycled" by being washed clean of their memories then shoved into a new life.

[Ralphe2449]

Not all people can awaken to the Echo, but whether that's because their souls are simply too "weak" post-Sundering to do so or if there's an actual distinction between different types of souls isn't really clear.

The starshowers in 5.3 produced a variety of reactions, with people either awakening to Echo proper, simply feeling a sense of sorrow and longing, or nothing at all, and I took the latter of the three as meaning their souls were ordinary personally; perhaps ones that were born after the Sundering because it's been mentioned souls are both created anew or simply "recycled" by being washed clean of their memories then shoved into a new life.

The other possibility could be that those pieces of souls have different aspects, the part of the soul that had the echo could likely been the part that lives on the 6th hence why the sundered soul of the 1st does not posses the echo for example but i dont think we have anything concrete either way. Though Elidibus did say when summoning WoLs on the first that he didnt need their soul to be whole, just to summon the "desire to vanquish evil" as if a part of the soul includes strong desires?

People of the source who have rejoined a few times would be more likely to have the echo since the have more parts of that soul

[TheMightyMollusk]

I thought people with the Echo were reincarnated souls from sundered Ancients, while those without it were newer souls. But I can't remember if that was ever official or just me extrapolating from incomplete info.