The problem with "retcon" or not is that from a player perspective - i.e. someone who doesn't have access to chats with high-up Frontier staff or their NDA-d material - there's really nothing to ... um ... "ret", because none of this made it into the game in the first place. It's more at the level of weird fan knowledge like "the writers considered having Season 3 of the Andromedaries have them fall through a wormhole to 24th century Achenar and even had some episodes drafted, but they eventually decided to go with the Eye of the Needle plot instead after negotiations with Hengist Duval fell through". So it can be really jarring if you're someone like Drew Wagar who does know that it was supposed to be leading up to a climatic duel between Bactrian and Marlin Duval atop the Imperial palace and all the foreshadowing you put into season 2's scripts about how he was really into "the real killer" conspiracies suddenly goes nowhere ... but if you're just watching the show-as-released and enjoying wacky camel hijinks you'd never know.
The original version of "The Club" was an ultra-secret conspiracy of various people. So secret, in fact, that their existence was never really hinted at in any in-game material. Sure, there were clearly conspiracies going on, but nothing that would require them all to be coordinated by the same shadowy group (and indeed the version shown in Premonition who were behind everything ... including things which really didn't need to be explained as the actions of a mysterious conspiracy ... in some ways seemed more of a "yeah, they were there all along" retcon of what had happened so far in game)
Similarly with the Thargoid factions. The "use human space to cover their escape" option was looking geographically implausible long before Premonition came out, and even on a more metaphorical level it's unclear why the Klaxians would stop to fight us long enough to let their actual target get away.
By the time in late 2017 when Frontier were definitely realising that "developing features" was going to take way longer than they originally thought ... well, even the much simpler and less complicated-plot-heavy Thargoid war we've currently got has been running pretty slowly to let the actual code catch up so that all the interesting stuff can happen in-game rather than the Titans being replaced by debris fields one Thursday with a Galnet article saying "after a heroic attack by Admiral Tanner's personal squadron, Taranis has been destroyed". And that's then required increasingly bizarre excuses for the Federal election process to stop Winters taking office until Powerplay is ready, etc. [1]
So given just how little of their plans they'd actually revealed ... the next writing team taking things in a different but still apparently compatible direction was really easy. And if the next team to pick up the plot wants to go back to some of the earlier stuff ...
- there's still potential for the Oresrians / Klaxians (whichever we don't currently see) to show up in some form with plenty of reasons why the earlier out-of-game sources were misunderstanding/deliberately lying for personal gain/etc.
- the Club can certainly stick around in a slightly reduced but still dangerous form as a conspiracy of Federal/Sirius corporate executives attempting to grow their military empires, but not behind absolutely everything; Imperial politics, Azimuth, the Consortium, etc. can all involve different competing conspiracies. Turning "well, it's the Club so we obviously oppose it" into "well, it's the Club, but they are fighting the Consortium on this one" is potentially very interesting
- Halsey may find it politically savvy to keep quiet about her visions nowadays, and Gan Romero's body may never be found, but the writing team could pick that up again any time. Well, any time that the development/art side of the team has had a good long lead-up to implement something cool for it to lead to, anyway!
- there's lots of other hooks to pick up on too: what were the League of Reparations really up to? will we ever find out more about the Dredger clans? is Winters stalling because the Winking Cat has stolen the Great Seal of the Federation so she can't be inaugurated, and both parties agree it'd be way too embarrassing if that news got out?
[1] I'm definitely coming from a perspective here where the Azimuth/NMLA storylines, precisely because they used existing in-game features (but creatively!) and therefore didn't have to wait too much for the rest of the team while they worked on Odyssey/post-Odyssey fixes, were I think the most solid era of Elite Dangerous storytelling in terms of "using Elite Dangerous to tell a story" (if you preferred some other thing for "story told in the Elite Dangerous setting", sure, we all have our personal favourites). I don't think it's entirely surprising that - like many of the things Frontier thought sounded cool in 2013 - actually implementing them into a game hasn't always turned out to work that way, and therefore some plans for future plot have changed to fit with "what can we actually do on-screen?".
