That's no small spoiler, considering what can be extrapolated...
For anyone who's seen the trailers, it's not a spoiler at all, given that the tweet tells us that, yep, what it looks like is about to happen in the trailers is in fact going to happen in the film. So, all that can be inferred after Ford's tweet could have been inferred before it. If you watch a trailer that depicts something as super-likely to happen, and then you have it confirmed that, yep, it happens, that's not a spoiler.
Now, for those who haven't seen the trailers, sure it's a spoiler.
Also, the tweet says nothing about what you've extrapolated. Your extrapolation is based on a theory about preproduction art, which is itself its own kind of spoiler. Again, that was already "spoiled" by looking at the trailers and making inferences regarding the art. Ford's tweet doesn't affect the extrapolations from the preproduction art one way or another. There's still nothing solid about what's going on in them in terms of what's in the film, same as before the tweet.