I think it might be time to bump this thread with new info about The Key from 7.3, and 7.4.
7.3
During the escape room puzzle section in the Preservation labs, we learned that the actual Key is the white crystal, and the rest is an electrope housing made my Preservation. There was also some documents that demonstrate the volatility of The Key during Preservation's early experiments on it.
"Nothing of note. The mystery of the key's activation condition remains unsolved.
The key triggered an explosion today. Temporary interdimensional portal verified. Continue attempts to stabilize the core's energy reactions.
Thirteen researchers sustained fatal injuries in the explosion. Memory faculties of four personnel sufficiently intact for Endless conversion. Remaining nine designated for aether reclamation processing.
Nothing of note. Rejected resignations of two Milalla researchers.
Major incident. Details in full report."
It describes The Key causing an explosion big enough to kill 13 scientists, and violent enough that most of the scientists could not become Endless as a result.
7.4
While no definitive answers were given, we did get some statements about The Key from a direct descendant of the original Speaker, Miayli, and rather ominous ones. Miayli is also Alayla's sister.
Miayli: But be that as it may, my sister gave up not only her life, but her darling daughter to prevent its misuse.
Miayli: They devoted their lives to understanding the key so that future generations would not be burdened by it.
Miayli: A word of caution, keeper of the key.
Miayli: As you know, it is a relic that has traveled across centuries and worlds, passing through countless hands...
Miayli: ...Oft beckoning to those ruled by ambition or avarice. Indeed, some have wondered if it chooses its master.
Miayli: But I believe differently. I believe that some inexorable force─call it “fate” if you will─ushers it from one bearer to the next.
Miayli: Be wary, for fate's regard now falls upon you.
At one point she asks the Warrior of Light what they would do with The Key if they can get it to work, and the player has dialog choices.
'Travel'
Miayli: For some, that might be a self-serving end. But your deeds are proof that I needn't worry.
'Herosim'
Miayli: For some, that might be a self-serving end. But your deeds are proof that I needn't worry.
'I don't know'
Miayli: The very fact that you don't have an answer is proof that you understand the weight of this power, and do not take it lightly.
The 'I don't know' option is the only one where Miayli has unique dialog.
While these are all Miayli's feelings, there doesn't seem to be a reason to doubt her given her relation to The Key. The Key seems as dangerous as ever, especially with the idea that it may have 'chosen' the Warrior of Light. Perhaps that is what was happening when the Azem symbol appeared on it at the start of the Queen Eternal fight. The idea of it being a burden, and not a gift is very much alive still.