Dark Eldar would be so jealous when they learn Tide can make organic bodies without problems while they make twisted caricatures of themselves.
Not all of them; Vect for instance has a whole system set up with the Haemonculi to fish his soul out of the Warp before Slaanesh gets it in the event of his death and stuff it into a new cloned body. This is how Vect has survived so many of the assassination attempts against him; he
didn't survive them, it just turns out that Vect is one of those people who doesn't die when they are killed.
The big problem with cloned Eldar bodies is that they have no soul, and thus are extremely vulnerable to daemonic possession, so you need special and expensive facilities to keep the clone isolated from the Warp until you stick a soul in it if you don't want it to spontaneously turn into a Chaos Spawn.
Regarding Kotov's STC conclusion, I always read that as the author trying to amp up the grimdark: The thing the Mechanicus have been searching for, the thing that will save the Imperium, has been sitting
right there under everyone's noses the entire time and they just don't even notice, or when they
do notice they lose the knowledge as soon as they disconnect! Everything that humanity ever needed is perpetually
juuust out of reach!
Hahahaha! So grimdark.
So yeah, I'd take it with a grain of salt. The Speranza having a full STC database I can believe, since it's implied to have been intentionally built as that from the start with the line "The knowledge of the Men of Gold and their ancient ancestors was encoded in its very bones, enmeshed within every diamond helix of its structure." (It may also be either a Warp entity or a C'tan shard.) But the idea that
every Ark Mechanicus is the same holds no water; the Mechanicus are bad but they aren't
that bad. Hell, Cawl has a not-AI running one of his Ark Mechanicus's, and if he's able to create a definitely-not-an-AI system that can run the entire ship, I find it highly implausible that he would be unable to notice the unused STC system sitting somewhere inside it.
The thing you gotta remember about 40k books is that there are so many authors that they often actively contradict each other, and GW's official stance on the matter is that every 40k book is from an in-universe perspective and thus may in fact be wrong. This affects the Mechanicus particularly badly, as in earlier works they really
were that bad and were depicted as basically tech-illiterate children who had no idea what they were doing. But as time passed GW writers realized that this made absolutely no sense and they've been slowly moving away from that depiction of the AdMech and more towards "they're actually really smart and competent but there are just some very major obstacles in their way, as well as the extreme limitations put upon them by the restrictions on AI." (Which is why Cawl is able to outperform the entire Mechanicus so completely, amazing what you can accomplish when you make extensive use of
AI copies I mean Lesser Cawls.)
Also interesting fact, from what I can find it looks like Cawl came into contact with the ship again and managed to convince the AI to join him.
Which would explain allot actually.
Not to my knowledge? You might be getting confused about how in Avenging Son one tech-priest hypes Cawl up by saying "they say he beat the Spirit of Eternity in a game of wits" with no further details. This is hearsay, and should be treated as such.
AFAIK, the Speranza was last seen heading towards Mars from the Halo Stars and was probably on the wrong side of the galaxy when the Big Rift opened up. Given the many unstable elements aboard it and the Chaos of the rift, it is likely that the ship has since disappeared into the Warp and will never be heard from again. Because grimdark.