Yes, USSs have been part of the game since 1.0.
Mission "wrinkles" have been introduced to the game after 1.0.
The system in which Raxxla is is quite obviously in the game since 1.0. Therefore Raxxla is in the game since 1.0 - the real question is how obvious is it/was it to find it.
Example: random system XYZ is Raxxla - without anything in that system to identify it as Raxxla players have no way to really find it, but it is in the game
(Raxxla is the journey, not the destination {the biggest myth in ED should never be found})
P.S.: "Raxxla is in the game" doesn't have to mean that there is a location named Raxxla in the game, the lore, the mythos Raxxla is in the game
TBH, I'm the worst person in the world for trying to analyse stuff like this 'cos a) I only bought ED just after 2.0 was released and b) I'm lousy at remembering obsolete things but I think it'd probably help narrow-down the possibilities if people DID pay more attention to what was possible in 1.0
I completely agree that when FDev say "Raxxla is in the game" they might simply be talking about the "concept" of Raxxla being in the game - Raxxla was a legend in Elite lore and it's a legend in ED too, therefore it's "in the game" in the same form that it exists in Elite lore.
Given the original nature of Raxxla (as a myth in Elite lore but not existing in-game) it'd certainly provide an elegant irony if it was only "in" ED in exactly the same way.
Alternatively, Raxxla could be "in the game" in the same way that, say, ELWs are "in the game" too.
They're there but we can't interact with them until FDev give us the tools to do so.
There's enough permit-locked areas within the bubble, and within individual systems, that FDev could simply have picked out a location for Raxxla but we don't get to interact with it until they allow it.
Lastly, I hate to make unpleasant accusations but I'm pretty sure there
are people who data-mine ED in order to locate new content.
In that case, it's actually a good thing Raxxla has been in the game since 1.0 - assuming it
is actually a physical thing within the game.
If Raxxla had been inserted, or changed, after 1.0, I suspect that somebody would have noticed changes to the code and investigated.
The fact this hasn't happened suggests that Raxxla
has either been "in the game" in a physical way, unchanged, since 1.0 or that it's only "in the game" as a myth.