I wonder if we can get an official statement on how the DLCs fit into the canon? If it's considered semi canon, I suppose I can live with that. I just don't want to see Fallout having to deal with extra terrestials in the future
That's going to be a rather personal matter any way you split it, though. For example, I actually consider most of Fallout Tactics to be "canon" except for areas where it's specifically contradicted elsewhere.
But yeah - I think the real crux of the matter has little to do with that actual DLC. And more about whether alien encounters ought to play a prominent role in the games moving forward from here. For myself even - I think I might have fun with this particular DLC - sort of as an extended Easter Egg encounter. I personally even consider those earlier alien encounters in Fallout 1 and 2 to be something that actually "happened" to my characters. But I would not want them to play a prominent role in things like Fallout 4 or anything like that.
ie, an Alien Companion, or an "Aliens vs Enclave" scenario would be going too far. I can concede aliens and flying saucers, and the occasional quick encounter being a close enough fit for Fallout. But having them play a major role in the game would be pushing it. If, while playing Fallout 4 - I come across a line of text saying that the whole Apocalypse was actually a clever Alien Master Plan for World Domination - that will be the last time I play a Fallout game.
(I doubt that would actually happen - but just as an example...)
They might fit the retrofuturistic setting, but they don't fit the theme of the Fallout series, which explores how humans survived the apocalypse.
I could see the potential for an alien encounter to provide another perspective to the whole situation. Just as a contrast to the human condition. Fallout being all about contrast, after all. I could see the potential for something like this to be handled in a very thoughtful and interesting way. Whether Bethesda lives up to that promise, or just provides the platform for lots of "Alien Probe" jokes, is another matter.
To the OP: One thing you might want to consider is that I would wager for most people, it's less about
whether Aliens and Flying Saucers fit into the setting through a rigid and critical look at existing canon and the Fallout Bible. And more about whether it
should be a prominent aspect of the game. And exactly how prominent a role that should be. I mean, Jar Jar Binks is canon. There's no getting away from that. But that doesn't mean it's a good thing...