hello, i just finished this game,
i'm still in the dark :)

was this whole process a trip within en's owns soul, like "matrix" ?
or was it real ?

We have
-Gramps
-Foster (is foster gramps ?)
-London (i suppose an AI, developped by foster, which hate foster but at the same time hates en for having killed foster)
i think i' m confusing a lot the gramps (grand pa ?) with foster.
-en, which is apparently one of the resourceful, meaning in my head, she's already a clone of somebody selected by gramps (or foster i'm lost)

what's the relationship between foster and en ? just simple love ? or something else
what was en : as a resourceful, she always boast being the most clever and rich, i see her as a rich corporation leader.

if everything is real, who build the palace ? Aliens lol ? for me, i prefer to think everything is real, since they arrived by spaceship.

is London (the AI) integrated into the skull of en, or in the armor ?

what are the "big clones" at the end of the game ?
the palace looks like unable to inovate, and suddenly, hey, i'm creating big clones of you that can do everything except using elevators, and jumping i suppose.

If there is a discussion thread somewhere, could you point it out :)
i feel that the story could be interesting, but really, as always, story designers give us only a very small glimpse of the story without enough details :/

Maybe that's just me, but I quite like it when the details of a story are purposefully left unexplained, giving the recipient (or the player in this case) the opportunity to either ponder and fill in the blanks with a version of her/his own or let it stand and accept it as "incomplete".
With ECHO I tend to fall into the latter category, meaning I'm content with what Ultra Ultra decided to reveal and give away over the course of the game. Sure, it would be nice having official and exhaustive answers to all those questions but I think those things are better left unexplained and clouded in mystery, at least for now. Who knows - if ECHO has done / still is doing well enough Ultra Ultra might consider a direct sequel (w/ Foster as the protagonist) or something different but in the same universe which then would delve further and deeper into the "lore" and eventually explain ALL the things.

Well, imho it's clear enough, but maybe that's because I kept the english voices instead of my native language's ones (french). However I will be using french in my next playthrough, since the voices seem to be pretty decent and deserve some recognition; I chose english first in fear of a bad translation, since that happens very often.

Now to the background

En is of a people called "The resourceful", of which the Grandfather seems to be some sort of a spiritual leader (I don't know however if he's a spiritual leader of all the Resourceful, or only a group of them). He prepares his followers to visiting a faraway palace, which only the best should succeed at, with promises of great rewards. Many people's lives have been sacrificed in the preparation ritual, and preparation includes gene selection. It looks like the ritual culminates in something called the "Translation" where one lays on some sort of a marble table, the body being absorbed by the table that produces a cube in return.

En didn't want to participate in the preparation and its hypothetic rewards and enjoy life instead. However she knew she had no choice, so she first accepted, knowing the first rituals would help her get stronger. Then she fled.

That's where Foster comes into play. The Grandfather hired him as a mercenary to find En and bring her back, which he did successfully. However, as the Grandfather was about to "Translate" her, he changed his mind and decided to free her. Then they fled together. Foster had been mortally wounded in the fight though, and En decided to translate him, in the hope she would then be able to bring him back to life in the palace. En had been wounded too. She came back to the ship with the Foster-cube and went into stasis for a hundred years, monitored by the ship's AI, London, with the palace as a destination.

(The palace coordinates seem to have been stolen from the Grandfather by Foster, or maybe En. London thinks that Foster has become cold and delusional with time, and didn't free En out of kindness, but rather because he was expecting riches in the process)

That's where the game begins

***** BEGIN SPOILERS *****

So, En goes through the challenges of the game and finally reaches her goal of saving Foster. There's a price to pay however, she will only be able to save him at the expense of her life, which she decides to sacrifice.

Foster wakes up in the palace, alive.

A little detail about the big golden clones : you said they don't use lifts, but they do use lifts. I experienced that myself...

***** END SPOILERS *****